Update 2-Working-With-Data/08-data-preparation/notebook.ipynb

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: leestott

2-Working-With-Data/08-data-preparation/notebook.ipynb

@@ -3919,8 +3919,11 @@
         "except ImportError:\n",
         "    print(\"scipy is required for Z-score calculation. Please install it with 'pip install scipy' and rerun this cell.\")\n",
         "else:\n",
-        "    # Calculate Z-scores for age\n",
-        "    dirty_data['age_zscore'] = np.abs(stats.zscore(dirty_data['age']))\n",
+        "    # Calculate Z-scores for age, handling NaN values\n",
+        "    age_nonan = dirty_data['age'].dropna()\n",
+        "    zscores = np.abs(stats.zscore(age_nonan))\n",
+        "    dirty_data['age_zscore'] = np.nan\n",
+        "    dirty_data.loc[age_nonan.index, 'age_zscore'] = zscores\n",
         "\n",
         "    # Typically, Z-score > 3 indicates an outlier\n",
         "    print(\"Rows with age Z-score > 3:\")\n",