diff --git a/notebooks/02_04b.ipynb b/notebooks/02_04b.ipynb
index 97411ce..65c41a2 100644
--- a/notebooks/02_04b.ipynb
+++ b/notebooks/02_04b.ipynb
@@ -10,7 +10,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": 2,
    "id": "5be0cfbf-e779-42b3-8bd6-f3dd46888ebb",
    "metadata": {},
    "outputs": [],
@@ -28,6 +28,915 @@
    "source": [
     "### Filling missing values using fillna(), replace() and interpolate()"
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "7a57182f",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "data = {'name': ['steve','john','richard','sarah','randy'\n",
+    "                 ,'micheal','julie']\n",
+    "        ,'age': [20,21,33,23,42,38,22]         \n",
+    "        ,'gender':['male','male','male','female','male'\n",
+    "                 ,'male','female']\n",
+    "        ,'rank':[2,1,3,5,4,7,6]         \n",
+    "                 }"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "id": "d162fd07",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "ranking_df = DataFrame(data)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "id": "8523dea0",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>name</th>\n",
+       "      <th>age</th>\n",
+       "      <th>gender</th>\n",
+       "      <th>rank</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>steve</td>\n",
+       "      <td>20</td>\n",
+       "      <td>male</td>\n",
+       "      <td>2</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>john</td>\n",
+       "      <td>21</td>\n",
+       "      <td>male</td>\n",
+       "      <td>1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>richard</td>\n",
+       "      <td>33</td>\n",
+       "      <td>male</td>\n",
+       "      <td>3</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>sarah</td>\n",
+       "      <td>23</td>\n",
+       "      <td>female</td>\n",
+       "      <td>5</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>randy</td>\n",
+       "      <td>42</td>\n",
+       "      <td>male</td>\n",
+       "      <td>4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>micheal</td>\n",
+       "      <td>38</td>\n",
+       "      <td>male</td>\n",
+       "      <td>7</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>julie</td>\n",
+       "      <td>22</td>\n",
+       "      <td>female</td>\n",
+       "      <td>6</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      name  age  gender  rank\n",
+       "0    steve   20    male     2\n",
+       "1     john   21    male     1\n",
+       "2  richard   33    male     3\n",
+       "3    sarah   23  female     5\n",
+       "4    randy   42    male     4\n",
+       "5  micheal   38    male     7\n",
+       "6    julie   22  female     6"
+      ]
+     },
+     "execution_count": 5,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "ranking_df"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "3044327f",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "ranking_df.iloc[2:5,1] = np.nan"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "id": "d1a1cc35",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "ranking_df.iloc[3:6,3] = np.nan"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "id": "26e68549",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>name</th>\n",
+       "      <th>age</th>\n",
+       "      <th>gender</th>\n",
+       "      <th>rank</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>steve</td>\n",
+       "      <td>20.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>2.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>john</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>1.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>richard</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>male</td>\n",
+       "      <td>3.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>sarah</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>female</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>randy</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>male</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>micheal</td>\n",
+       "      <td>38.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>julie</td>\n",
+       "      <td>22.0</td>\n",
+       "      <td>female</td>\n",
+       "      <td>6.0</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      name   age  gender  rank\n",
+       "0    steve  20.0    male   2.0\n",
+       "1     john  21.0    male   1.0\n",
+       "2  richard   NaN    male   3.0\n",
+       "3    sarah   NaN  female   NaN\n",
+       "4    randy   NaN    male   NaN\n",
+       "5  micheal  38.0    male   NaN\n",
+       "6    julie  22.0  female   6.0"
+      ]
+     },
+     "execution_count": 8,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "ranking_df"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "id": "6f22e0fc",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "name      0\n",
+       "age       3\n",
+       "gender    0\n",
+       "rank      3\n",
+       "dtype: int64"
+      ]
+     },
+     "execution_count": 9,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "ranking_df.isnull().sum()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "id": "fe95be53",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "name      7\n",
+       "age       4\n",
+       "gender    7\n",
+       "rank      4\n",
+       "dtype: int64"
+      ]
+     },
+     "execution_count": 12,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "ranking_df.notnull().sum()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 13,
+   "id": "997479d9",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>name</th>\n",
+       "      <th>age</th>\n",
+       "      <th>gender</th>\n",
+       "      <th>rank</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>richard</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>male</td>\n",
+       "      <td>3.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>sarah</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>female</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>randy</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>male</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      name  age  gender  rank\n",
+       "2  richard  NaN    male   3.0\n",
+       "3    sarah  NaN  female   NaN\n",
+       "4    randy  NaN    male   NaN"
+      ]
+     },
+     "execution_count": 13,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "bool_series = pd.isnull(ranking_df['age'])\n",
+    "ranking_df[bool_series]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 14,
+   "id": "0ed33a94",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>name</th>\n",
+       "      <th>age</th>\n",
+       "      <th>gender</th>\n",
+       "      <th>rank</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>steve</td>\n",
+       "      <td>20.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>2.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>john</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>1.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>richard</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>male</td>\n",
+       "      <td>3.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>sarah</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>female</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>randy</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>male</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>micheal</td>\n",
+       "      <td>38.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>julie</td>\n",
+       "      <td>22.0</td>\n",
+       "      <td>female</td>\n",
+       "      <td>6.0</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      name   age  gender  rank\n",
+       "0    steve  20.0    male   2.0\n",
+       "1     john  21.0    male   1.0\n",
+       "2  richard   NaN    male   3.0\n",
+       "3    sarah   NaN  female   NaN\n",
+       "4    randy   NaN    male   NaN\n",
+       "5  micheal  38.0    male   NaN\n",
+       "6    julie  22.0  female   6.0"
+      ]
+     },
+     "execution_count": 14,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "ranking_df"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 18,
+   "id": "25909be7",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "test = ranking_df.fillna(0)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 24,
+   "id": "a37e370a",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>name</th>\n",
+       "      <th>age</th>\n",
+       "      <th>gender</th>\n",
+       "      <th>rank</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>steve</td>\n",
+       "      <td>20.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>2.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>john</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>1.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>richard</td>\n",
+       "      <td>38.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>3.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>sarah</td>\n",
+       "      <td>38.0</td>\n",
+       "      <td>female</td>\n",
+       "      <td>6.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>randy</td>\n",
+       "      <td>38.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>6.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>micheal</td>\n",
+       "      <td>38.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>6.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>julie</td>\n",
+       "      <td>22.0</td>\n",
+       "      <td>female</td>\n",
+       "      <td>6.0</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      name   age  gender  rank\n",
+       "0    steve  20.0    male   2.0\n",
+       "1     john  21.0    male   1.0\n",
+       "2  richard  38.0    male   3.0\n",
+       "3    sarah  38.0  female   6.0\n",
+       "4    randy  38.0    male   6.0\n",
+       "5  micheal  38.0    male   6.0\n",
+       "6    julie  22.0  female   6.0"
+      ]
+     },
+     "execution_count": 24,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "test = ranking_df.bfill()\n",
+    "test"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 25,
+   "id": "e53a3117",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>name</th>\n",
+       "      <th>age</th>\n",
+       "      <th>gender</th>\n",
+       "      <th>rank</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>steve</td>\n",
+       "      <td>20.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>2.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>john</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>1.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>richard</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>3.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>sarah</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>female</td>\n",
+       "      <td>3.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>randy</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>3.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>micheal</td>\n",
+       "      <td>38.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>3.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>julie</td>\n",
+       "      <td>22.0</td>\n",
+       "      <td>female</td>\n",
+       "      <td>6.0</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      name   age  gender  rank\n",
+       "0    steve  20.0    male   2.0\n",
+       "1     john  21.0    male   1.0\n",
+       "2  richard  21.0    male   3.0\n",
+       "3    sarah  21.0  female   3.0\n",
+       "4    randy  21.0    male   3.0\n",
+       "5  micheal  38.0    male   3.0\n",
+       "6    julie  22.0  female   6.0"
+      ]
+     },
+     "execution_count": 25,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "test = ranking_df.ffill()\n",
+    "test"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 30,
+   "id": "a5eafedb",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>name</th>\n",
+       "      <th>age</th>\n",
+       "      <th>gender</th>\n",
+       "      <th>rank</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>steve</td>\n",
+       "      <td>20.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>2.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>john</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>1.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>julie</td>\n",
+       "      <td>22.0</td>\n",
+       "      <td>female</td>\n",
+       "      <td>6.0</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "    name   age  gender  rank\n",
+       "0  steve  20.0    male   2.0\n",
+       "1   john  21.0    male   1.0\n",
+       "6  julie  22.0  female   6.0"
+      ]
+     },
+     "execution_count": 30,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "ranking_df.dropna()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 31,
+   "id": "a82b2b07",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>name</th>\n",
+       "      <th>age</th>\n",
+       "      <th>gender</th>\n",
+       "      <th>rank</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>steve</td>\n",
+       "      <td>20.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>2.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>john</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>1.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>richard</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>male</td>\n",
+       "      <td>3.0</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>sarah</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>female</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>randy</td>\n",
+       "      <td>NaN</td>\n",
+       "      <td>male</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>micheal</td>\n",
+       "      <td>38.0</td>\n",
+       "      <td>male</td>\n",
+       "      <td>NaN</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>julie</td>\n",
+       "      <td>22.0</td>\n",
+       "      <td>female</td>\n",
+       "      <td>6.0</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "      name   age  gender  rank\n",
+       "0    steve  20.0    male   2.0\n",
+       "1     john  21.0    male   1.0\n",
+       "2  richard   NaN    male   3.0\n",
+       "3    sarah   NaN  female   NaN\n",
+       "4    randy   NaN    male   NaN\n",
+       "5  micheal  38.0    male   NaN\n",
+       "6    julie  22.0  female   6.0"
+      ]
+     },
+     "execution_count": 31,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "ranking_df.dropna(how='all')"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "7a809d4c",
+   "metadata": {},
+   "outputs": [],
+   "source": []
   }
  ],
  "metadata": {
@@ -46,7 +955,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.8"
+   "version": "3.12.1"
   }
  },
  "nbformat": 4,
diff --git a/notebooks/02_04e.ipynb b/notebooks/02_04e.ipynb
index 66aa5ef..ee800ab 100644
--- a/notebooks/02_04e.ipynb
+++ b/notebooks/02_04e.ipynb
@@ -10,7 +10,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": 1,
    "id": "5be0cfbf-e779-42b3-8bd6-f3dd46888ebb",
    "metadata": {},
    "outputs": [],
@@ -31,7 +31,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": 2,
    "metadata": {},
    "outputs": [
     {
@@ -126,7 +126,7 @@
        "6    julie  22.0  Female   6.0"
       ]
      },
-     "execution_count": 4,
+     "execution_count": 2,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -146,7 +146,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 3,
    "metadata": {},
    "outputs": [
     {
@@ -241,7 +241,7 @@
        "6  False  False   False  False"
       ]
      },
-     "execution_count": 5,
+     "execution_count": 3,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -252,7 +252,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": 4,
    "metadata": {},
    "outputs": [
     {
@@ -347,7 +347,7 @@
        "6   True   True    True   True"
       ]
      },
-     "execution_count": 6,
+     "execution_count": 4,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -358,7 +358,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": 5,
    "metadata": {},
    "outputs": [
     {
@@ -421,7 +421,7 @@
        "4    randy  NaN   Male   NaN"
       ]
      },
-     "execution_count": 7,
+     "execution_count": 5,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -433,7 +433,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 8,
+   "execution_count": 6,
    "metadata": {},
    "outputs": [
     {
@@ -528,7 +528,7 @@
        "6    julie  22.0  Female   6.0"
       ]
      },
-     "execution_count": 8,
+     "execution_count": 6,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -539,17 +539,9 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 9,
+   "execution_count": 8,
    "metadata": {},
    "outputs": [
-    {
-     "name": "stderr",
-     "output_type": "stream",
-     "text": [
-      "/tmp/ipykernel_29111/2647120121.py:1: FutureWarning: DataFrame.fillna with 'method' is deprecated and will raise in a future version. Use obj.ffill() or obj.bfill() instead.\n",
-      "  ranking_df.fillna(method='pad')\n"
-     ]
-    },
     {
      "data": {
       "text/html": [
@@ -595,30 +587,30 @@
        "    <tr>\n",
        "      <th>2</th>\n",
        "      <td>richard</td>\n",
-       "      <td>22.0</td>\n",
+       "      <td>23.0</td>\n",
        "      <td>Male</td>\n",
        "      <td>4.0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>3</th>\n",
-       "      <td>richard</td>\n",
-       "      <td>22.0</td>\n",
+       "      <td>randy</td>\n",
+       "      <td>23.0</td>\n",
        "      <td>Male</td>\n",
-       "      <td>4.0</td>\n",
+       "      <td>6.0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>4</th>\n",
        "      <td>randy</td>\n",
-       "      <td>22.0</td>\n",
+       "      <td>23.0</td>\n",
        "      <td>Male</td>\n",
-       "      <td>4.0</td>\n",
+       "      <td>6.0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>5</th>\n",
        "      <td>micheal</td>\n",
        "      <td>23.0</td>\n",
        "      <td>Male</td>\n",
-       "      <td>4.0</td>\n",
+       "      <td>6.0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>6</th>\n",
@@ -635,35 +627,27 @@
        "     names   age  gender  rank\n",
        "0    steve  20.0    Male   2.0\n",
        "1     john  22.0    Male   1.0\n",
-       "2  richard  22.0    Male   4.0\n",
-       "3  richard  22.0    Male   4.0\n",
-       "4    randy  22.0    Male   4.0\n",
-       "5  micheal  23.0    Male   4.0\n",
+       "2  richard  23.0    Male   4.0\n",
+       "3    randy  23.0    Male   6.0\n",
+       "4    randy  23.0    Male   6.0\n",
+       "5  micheal  23.0    Male   6.0\n",
        "6    julie  22.0  Female   6.0"
       ]
      },
-     "execution_count": 9,
+     "execution_count": 8,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "ranking_df.fillna(method='pad')"
+    "ranking_df.bfill()"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 10,
+   "execution_count": 9,
    "metadata": {},
    "outputs": [
-    {
-     "name": "stderr",
-     "output_type": "stream",
-     "text": [
-      "/tmp/ipykernel_29111/3253257716.py:1: FutureWarning: DataFrame.fillna with 'method' is deprecated and will raise in a future version. Use obj.ffill() or obj.bfill() instead.\n",
-      "  ranking_df.fillna(method='bfill')\n"
-     ]
-    },
     {
      "data": {
       "text/html": [
@@ -709,30 +693,30 @@
        "    <tr>\n",
        "      <th>2</th>\n",
        "      <td>richard</td>\n",
-       "      <td>23.0</td>\n",
+       "      <td>22.0</td>\n",
        "      <td>Male</td>\n",
        "      <td>4.0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>3</th>\n",
-       "      <td>randy</td>\n",
-       "      <td>23.0</td>\n",
+       "      <td>richard</td>\n",
+       "      <td>22.0</td>\n",
        "      <td>Male</td>\n",
-       "      <td>6.0</td>\n",
+       "      <td>4.0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>4</th>\n",
        "      <td>randy</td>\n",
-       "      <td>23.0</td>\n",
+       "      <td>22.0</td>\n",
        "      <td>Male</td>\n",
-       "      <td>6.0</td>\n",
+       "      <td>4.0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>5</th>\n",
        "      <td>micheal</td>\n",
        "      <td>23.0</td>\n",
        "      <td>Male</td>\n",
-       "      <td>6.0</td>\n",
+       "      <td>4.0</td>\n",
        "    </tr>\n",
        "    <tr>\n",
        "      <th>6</th>\n",
@@ -749,20 +733,20 @@
        "     names   age  gender  rank\n",
        "0    steve  20.0    Male   2.0\n",
        "1     john  22.0    Male   1.0\n",
-       "2  richard  23.0    Male   4.0\n",
-       "3    randy  23.0    Male   6.0\n",
-       "4    randy  23.0    Male   6.0\n",
-       "5  micheal  23.0    Male   6.0\n",
+       "2  richard  22.0    Male   4.0\n",
+       "3  richard  22.0    Male   4.0\n",
+       "4    randy  22.0    Male   4.0\n",
+       "5  micheal  23.0    Male   4.0\n",
        "6    julie  22.0  Female   6.0"
       ]
      },
-     "execution_count": 10,
+     "execution_count": 9,
      "metadata": {},
      "output_type": "execute_result"
     }
    ],
    "source": [
-    "ranking_df.fillna(method='bfill')"
+    "ranking_df.ffill()"
    ]
   },
   {
@@ -1218,7 +1202,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.13"
+   "version": "3.12.1"
   }
  },
  "nbformat": 4,
diff --git a/notebooks/02_05b.ipynb b/notebooks/02_05b.ipynb
index 79444cd..f3583dd 100644
--- a/notebooks/02_05b.ipynb
+++ b/notebooks/02_05b.ipynb
@@ -19,6 +19,134 @@
     "### Removing duplicates"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>column 1</th>\n",
+       "      <th>column 2</th>\n",
+       "      <th>column 3</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>1</td>\n",
+       "      <td>a</td>\n",
+       "      <td>A</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>1</td>\n",
+       "      <td>a</td>\n",
+       "      <td>A</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>2</td>\n",
+       "      <td>b</td>\n",
+       "      <td>B</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>2</td>\n",
+       "      <td>b</td>\n",
+       "      <td>B</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>3</td>\n",
+       "      <td>c</td>\n",
+       "      <td>C</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>5</th>\n",
+       "      <td>3</td>\n",
+       "      <td>c</td>\n",
+       "      <td>C</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>3</td>\n",
+       "      <td>c</td>\n",
+       "      <td>C</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "   column 1 column 2 column 3\n",
+       "0         1        a        A\n",
+       "1         1        a        A\n",
+       "2         2        b        B\n",
+       "3         2        b        B\n",
+       "4         3        c        C\n",
+       "5         3        c        C\n",
+       "6         3        c        C"
+      ]
+     },
+     "execution_count": 2,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "DF_obj = DataFrame({'column 1': [1,1,2,2,3,3,3],\n",
+    "                    'column 2':['a', 'a', 'b', 'b', 'c', 'c', 'c'],\n",
+    "                    'column 3': ['A', 'A', 'B', 'B', 'C', 'C', 'C']})\n",
+    "DF_obj"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/plain": [
+       "0    False\n",
+       "1     True\n",
+       "2    False\n",
+       "3     True\n",
+       "4    False\n",
+       "5     True\n",
+       "6     True\n",
+       "dtype: bool"
+      ]
+     },
+     "execution_count": 3,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "DF_obj.duplicated()"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
@@ -44,7 +172,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.8.8"
+   "version": "3.12.1"
   }
  },
  "nbformat": 4,
diff --git a/notebooks/02_06e.ipynb b/notebooks/02_06e.ipynb
index 0c8562f..34bbb5c 100644
--- a/notebooks/02_06e.ipynb
+++ b/notebooks/02_06e.ipynb
@@ -1381,7 +1381,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.13"
+   "version": "3.12.1"
   }
  },
  "nbformat": 4,
diff --git a/notebooks/02_07b.ipynb b/notebooks/02_07b.ipynb
index 8877c57..c769c56 100644
--- a/notebooks/02_07b.ipynb
+++ b/notebooks/02_07b.ipynb
@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": 2,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -17,6 +17,283 @@
    "source": [
     "### Grouping data by column index"
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>car_names</th>\n",
+       "      <th>mpg</th>\n",
+       "      <th>cyl</th>\n",
+       "      <th>disp</th>\n",
+       "      <th>hp</th>\n",
+       "      <th>drat</th>\n",
+       "      <th>wt</th>\n",
+       "      <th>qsec</th>\n",
+       "      <th>vs</th>\n",
+       "      <th>am</th>\n",
+       "      <th>gear</th>\n",
+       "      <th>carb</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>0</th>\n",
+       "      <td>Mazda RX4</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>6</td>\n",
+       "      <td>160.0</td>\n",
+       "      <td>110</td>\n",
+       "      <td>3.90</td>\n",
+       "      <td>2.620</td>\n",
+       "      <td>16.46</td>\n",
+       "      <td>0</td>\n",
+       "      <td>1</td>\n",
+       "      <td>4</td>\n",
+       "      <td>4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>1</th>\n",
+       "      <td>Mazda RX4 Wag</td>\n",
+       "      <td>21.0</td>\n",
+       "      <td>6</td>\n",
+       "      <td>160.0</td>\n",
+       "      <td>110</td>\n",
+       "      <td>3.90</td>\n",
+       "      <td>2.875</td>\n",
+       "      <td>17.02</td>\n",
+       "      <td>0</td>\n",
+       "      <td>1</td>\n",
+       "      <td>4</td>\n",
+       "      <td>4</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>2</th>\n",
+       "      <td>Datsun 710</td>\n",
+       "      <td>22.8</td>\n",
+       "      <td>4</td>\n",
+       "      <td>108.0</td>\n",
+       "      <td>93</td>\n",
+       "      <td>3.85</td>\n",
+       "      <td>2.320</td>\n",
+       "      <td>18.61</td>\n",
+       "      <td>1</td>\n",
+       "      <td>1</td>\n",
+       "      <td>4</td>\n",
+       "      <td>1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>3</th>\n",
+       "      <td>Hornet 4 Drive</td>\n",
+       "      <td>21.4</td>\n",
+       "      <td>6</td>\n",
+       "      <td>258.0</td>\n",
+       "      <td>110</td>\n",
+       "      <td>3.08</td>\n",
+       "      <td>3.215</td>\n",
+       "      <td>19.44</td>\n",
+       "      <td>1</td>\n",
+       "      <td>0</td>\n",
+       "      <td>3</td>\n",
+       "      <td>1</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>Hornet Sportabout</td>\n",
+       "      <td>18.7</td>\n",
+       "      <td>8</td>\n",
+       "      <td>360.0</td>\n",
+       "      <td>175</td>\n",
+       "      <td>3.15</td>\n",
+       "      <td>3.440</td>\n",
+       "      <td>17.02</td>\n",
+       "      <td>0</td>\n",
+       "      <td>0</td>\n",
+       "      <td>3</td>\n",
+       "      <td>2</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "           car_names   mpg  cyl   disp   hp  drat     wt   qsec  vs  am  gear  \\\n",
+       "0          Mazda RX4  21.0    6  160.0  110  3.90  2.620  16.46   0   1     4   \n",
+       "1      Mazda RX4 Wag  21.0    6  160.0  110  3.90  2.875  17.02   0   1     4   \n",
+       "2         Datsun 710  22.8    4  108.0   93  3.85  2.320  18.61   1   1     4   \n",
+       "3     Hornet 4 Drive  21.4    6  258.0  110  3.08  3.215  19.44   1   0     3   \n",
+       "4  Hornet Sportabout  18.7    8  360.0  175  3.15  3.440  17.02   0   0     3   \n",
+       "\n",
+       "   carb  \n",
+       "0     4  \n",
+       "1     4  \n",
+       "2     1  \n",
+       "3     1  \n",
+       "4     2  "
+      ]
+     },
+     "execution_count": 3,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "address = '/workspaces/python-for-data-science-and-machine-learning-essential-training-part-1-3006708/data/mtcars.csv'\n",
+    "\n",
+    "cars = pd.read_csv(address)\n",
+    "\n",
+    "cars.columns = ['car_names','mpg','cyl','disp', 'hp', 'drat', 'wt', 'qsec', 'vs', 'am', 'gear', 'carb']\n",
+    "\n",
+    "cars.head()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe tbody tr th {\n",
+       "        vertical-align: top;\n",
+       "    }\n",
+       "\n",
+       "    .dataframe thead th {\n",
+       "        text-align: right;\n",
+       "    }\n",
+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>mpg</th>\n",
+       "      <th>disp</th>\n",
+       "      <th>hp</th>\n",
+       "      <th>drat</th>\n",
+       "      <th>wt</th>\n",
+       "      <th>qsec</th>\n",
+       "      <th>vs</th>\n",
+       "      <th>am</th>\n",
+       "      <th>gear</th>\n",
+       "      <th>carb</th>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>cyl</th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "      <th></th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>4</th>\n",
+       "      <td>26.663636</td>\n",
+       "      <td>105.136364</td>\n",
+       "      <td>82.636364</td>\n",
+       "      <td>4.070909</td>\n",
+       "      <td>2.285727</td>\n",
+       "      <td>19.137273</td>\n",
+       "      <td>0.909091</td>\n",
+       "      <td>0.727273</td>\n",
+       "      <td>4.090909</td>\n",
+       "      <td>1.545455</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>6</th>\n",
+       "      <td>19.742857</td>\n",
+       "      <td>183.314286</td>\n",
+       "      <td>122.285714</td>\n",
+       "      <td>3.585714</td>\n",
+       "      <td>3.117143</td>\n",
+       "      <td>17.977143</td>\n",
+       "      <td>0.571429</td>\n",
+       "      <td>0.428571</td>\n",
+       "      <td>3.857143</td>\n",
+       "      <td>3.428571</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>8</th>\n",
+       "      <td>15.100000</td>\n",
+       "      <td>353.100000</td>\n",
+       "      <td>209.214286</td>\n",
+       "      <td>3.229286</td>\n",
+       "      <td>3.999214</td>\n",
+       "      <td>16.772143</td>\n",
+       "      <td>0.000000</td>\n",
+       "      <td>0.142857</td>\n",
+       "      <td>3.285714</td>\n",
+       "      <td>3.500000</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "           mpg        disp          hp      drat        wt       qsec  \\\n",
+       "cyl                                                                     \n",
+       "4    26.663636  105.136364   82.636364  4.070909  2.285727  19.137273   \n",
+       "6    19.742857  183.314286  122.285714  3.585714  3.117143  17.977143   \n",
+       "8    15.100000  353.100000  209.214286  3.229286  3.999214  16.772143   \n",
+       "\n",
+       "           vs        am      gear      carb  \n",
+       "cyl                                          \n",
+       "4    0.909091  0.727273  4.090909  1.545455  \n",
+       "6    0.571429  0.428571  3.857143  3.428571  \n",
+       "8    0.000000  0.142857  3.285714  3.500000  "
+      ]
+     },
+     "execution_count": 4,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "cars_groups = cars.groupby(cars['cyl'])\n",
+    "cars_groups.mean(numeric_only=True)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
   }
  ],
  "metadata": {
@@ -35,7 +312,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.1"
+   "version": "3.12.1"
   }
  },
  "nbformat": 4,
diff --git a/notebooks/02_07e.ipynb b/notebooks/02_07e.ipynb
index 57a29e5..f21c71d 100644
--- a/notebooks/02_07e.ipynb
+++ b/notebooks/02_07e.ipynb
@@ -20,7 +20,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": null,
    "metadata": {},
    "outputs": [
     {
diff --git a/notebooks/02__03b.ipynb b/notebooks/02__03b.ipynb
index 75d4a75..1843e26 100644
--- a/notebooks/02__03b.ipynb
+++ b/notebooks/02__03b.ipynb
@@ -9,10 +9,41 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 1,
    "id": "acd063a4",
    "metadata": {},
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Requirement already satisfied: pip in /usr/local/python/3.12.1/lib/python3.12/site-packages (25.3)\n",
+      "Collecting pip\n",
+      "  Downloading pip-26.0.1-py3-none-any.whl.metadata (4.7 kB)\n",
+      "Downloading pip-26.0.1-py3-none-any.whl (1.8 MB)\n",
+      "\u001b[2K   \u001b[90m━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━\u001b[0m \u001b[32m1.8/1.8 MB\u001b[0m \u001b[31m36.5 MB/s\u001b[0m  \u001b[33m0:00:00\u001b[0m\n",
+      "\u001b[?25hInstalling collected packages: pip\n",
+      "  Attempting uninstall: pip\n",
+      "    Found existing installation: pip 25.3\n",
+      "    Uninstalling pip-25.3:\n",
+      "      Successfully uninstalled pip-25.3\n",
+      "Successfully installed pip-26.0.1\n",
+      "Collecting pandas\n",
+      "  Downloading pandas-3.0.1-cp312-cp312-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl.metadata (79 kB)\n",
+      "Collecting numpy>=1.26.0 (from pandas)\n",
+      "  Downloading numpy-2.4.2-cp312-cp312-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl.metadata (6.6 kB)\n",
+      "Requirement already satisfied: python-dateutil>=2.8.2 in /home/codespace/.local/lib/python3.12/site-packages (from pandas) (2.9.0.post0)\n",
+      "Requirement already satisfied: six>=1.5 in /home/codespace/.local/lib/python3.12/site-packages (from python-dateutil>=2.8.2->pandas) (1.17.0)\n",
+      "Downloading pandas-3.0.1-cp312-cp312-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl (10.9 MB)\n",
+      "\u001b[2K   \u001b[90m━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━\u001b[0m \u001b[32m10.9/10.9 MB\u001b[0m \u001b[31m25.6 MB/s\u001b[0m  \u001b[33m0:00:00\u001b[0m6m0:00:01\u001b[0m\n",
+      "\u001b[?25hDownloading numpy-2.4.2-cp312-cp312-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl (16.6 MB)\n",
+      "\u001b[2K   \u001b[90m━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━\u001b[0m \u001b[32m16.6/16.6 MB\u001b[0m \u001b[31m73.9 MB/s\u001b[0m  \u001b[33m0:00:00\u001b[0m6m0:00:01\u001b[0m\n",
+      "\u001b[?25hInstalling collected packages: numpy, pandas\n",
+      "\u001b[2K   \u001b[90m━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━\u001b[0m \u001b[32m2/2\u001b[0m [pandas]2m1/2\u001b[0m [pandas]\n",
+      "\u001b[1A\u001b[2KSuccessfully installed numpy-2.4.2 pandas-3.0.1\n"
+     ]
+    }
+   ],
    "source": [
     "!pip install --upgrade pip \n",
     "!pip install pandas "
@@ -25,6 +56,634 @@
    "source": [
     "#### Comparison operators (> < = <= => == !=) and Masking."
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "id": "6b6736e3",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import pandas as pd\n",
+    "import numpy as np"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "id": "0710cd0e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from pandas import DataFrame"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "a3028931",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "numbers_df = DataFrame(np.arange(0,90,3).reshape(10,3)\n",
+    "                       , index=['row 1','row 2','row 3','row 4','row 5','row 6','row 7','row 8','row 9','row 10']\n",
+    "                       , columns=['column 1','column 2','column 3'])"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "id": "5833bb4a",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<div>\n",
+       "<style scoped>\n",
+       "    .dataframe tbody tr th:only-of-type {\n",
+       "        vertical-align: middle;\n",
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+       "\n",
+       "    .dataframe tbody tr th {\n",
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+       "\n",
+       "    .dataframe thead th {\n",
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+       "</style>\n",
+       "<table border=\"1\" class=\"dataframe\">\n",
+       "  <thead>\n",
+       "    <tr style=\"text-align: right;\">\n",
+       "      <th></th>\n",
+       "      <th>column 1</th>\n",
+       "      <th>column 2</th>\n",
+       "      <th>column 3</th>\n",
+       "    </tr>\n",
+       "  </thead>\n",
+       "  <tbody>\n",
+       "    <tr>\n",
+       "      <th>row 1</th>\n",
+       "      <td>0</td>\n",
+       "      <td>3</td>\n",
+       "      <td>6</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>row 2</th>\n",
+       "      <td>9</td>\n",
+       "      <td>12</td>\n",
+       "      <td>15</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>row 3</th>\n",
+       "      <td>18</td>\n",
+       "      <td>21</td>\n",
+       "      <td>24</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>row 4</th>\n",
+       "      <td>27</td>\n",
+       "      <td>30</td>\n",
+       "      <td>33</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>row 5</th>\n",
+       "      <td>36</td>\n",
+       "      <td>39</td>\n",
+       "      <td>42</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>row 6</th>\n",
+       "      <td>45</td>\n",
+       "      <td>48</td>\n",
+       "      <td>51</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>row 7</th>\n",
+       "      <td>54</td>\n",
+       "      <td>57</td>\n",
+       "      <td>60</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
+       "      <th>row 8</th>\n",
+       "      <td>63</td>\n",
+       "      <td>66</td>\n",
+       "      <td>69</td>\n",
+       "    </tr>\n",
+       "    <tr>\n",
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+       "        column 1  column 2  column 3\n",
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+    "numbers_df"
+   ]
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+   "cell_type": "code",
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+   "id": "0775fe46",
+   "metadata": {},
+   "outputs": [
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+       "np.int64(3)"
+      ]
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+   ]
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+   "id": "bcecc000",
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+    "numbers_df.iloc[0,1] =20"
+   ]
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+      ]
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+    "numbers_df"
+   ]
+  },
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+   "id": "7dca7a2d",
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+    "numbers_df.iloc[[1,2,3],[1,2]]"
+   ]
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+       "    </tr>\n",
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+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "        column 1  column 2  column 3\n",
+       "row 1      False     False     False\n",
+       "row 2      False     False     False\n",
+       "row 3      False     False     False\n",
+       "row 4      False     False      True\n",
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+       "row 8       True      True      True\n",
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+       "row 10      True      True      True"
+      ]
+     },
+     "execution_count": 14,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "mask = numbers_df>30\n",
+    "mask"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 15,
+   "id": "234ed7c9",
+   "metadata": {},
+   "outputs": [
+    {
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+       "      <th>row 10</th>\n",
+       "      <td>81.0</td>\n",
+       "      <td>84.0</td>\n",
+       "      <td>87.0</td>\n",
+       "    </tr>\n",
+       "  </tbody>\n",
+       "</table>\n",
+       "</div>"
+      ],
+      "text/plain": [
+       "        column 1  column 2  column 3\n",
+       "row 1        NaN       NaN       NaN\n",
+       "row 2        NaN       NaN       NaN\n",
+       "row 3        NaN       NaN       NaN\n",
+       "row 4        NaN       NaN      33.0\n",
+       "row 5       36.0      39.0      42.0\n",
+       "row 6       45.0      48.0      51.0\n",
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+       "row 9       72.0      75.0      78.0\n",
+       "row 10      81.0      84.0      87.0"
+      ]
+     },
+     "execution_count": 15,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "numbers_df[mask]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "a6bdbad8",
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "e8b88c21",
+   "metadata": {},
+   "outputs": [],
+   "source": []
   }
  ],
  "metadata": {