added exercises

Author: trayc7

_episodes/07-additional-exercises.md

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+---
+title: Additional Exercises
+teaching: 1
+exercises: 0
+questions:
+- "Practice your python."
+objectives:
+- "Work on some python exercises to continue building your skills."
+keypoints:
+- "Practice makes Python."
+---
+
+
+# Python Practice
+
+The key to building your skills as a programmer is _practice_. Try giving yourself challenges to use the Python tools we have learned in class. Here are some exercises for you to work through to continue working on becoming a Pythonista. 
+
+## Python Datatypes
+
+1. Create a list in python `x = list(range(1,20))`. This will make a list of numbers from 1 to 20. Now try the following with this list:
+    1. Create a new list containing every 2nd element starting with element `x[1]`.
+    2. Print the last 8 values in the list to screen. 
+    3. Write a `for` loop to print each value, one at a time. 
+    4. Write a function that converts the entire list to a single string.
+
+2. Create 3 dictionaries:
+```
+d1 = {'a': 10, 'b': 20, 'c': 30}
+d1 = {'d': 40, 'e': 50}
+d1 = {'f': 60, 'g': 70, 'h': 80}
+```
+    1. Concatenate the dictionaries into one single dictionary called `my_dictionary`
+    2. Check to see if `my_dictionary` has the key `i`. 
+    3. Change the value associated with key `d` to `40.4`
+
+## Math
+
+1. Use the Numpy package to draw 100 random variables from a normal distribution with mean = 5 and standard deviation = 1. Assign these to a list called `norm_rvs`.
+2. Use Numpy to compute the sum of the list `x` crated in the very first exercise. 
+3. Write a function that takes the list `norm_rvs` and returns a list where each element is the `log(norm_rvs[i])`.
+4. Use the seaborn package to view histograms of `norm_rvs` and the log-transformed values. 
+
+## Pandas
+
+1. Load the CSV file from our previous exercises: `surveys_df = pd.read_csv("surveys.csv")`
+    1. Create a new dataframe variable called `surveys1997` containing only the observations from the year 1997.
+    2. Use a `for` loop to iterate over `surveys1997` and print the plot number to screen.
+
+
+<br>
+
+