Improve your Data Science skills and learn Python by attempting a code challenge. Get hints and view solutions if you get stuck.

Python Code Challenges for Data Scientists

There so are many interesting ways to solve FizzBuzz! We'll be crowd-sourcing some of the most creative solutions and adding them here over time. 

Below is an example of one of the most common approaches, however, there are many methods that are faster, and more concise than this solution.

FizzBuzz is one of the best-known code challenges in the world. Solving it with vanilla Python is fine. But things get spicy when other Python packages get involved.

FizzBuzz Code Challenge in Python with NumPy and Pandas

FizzBuzz

### Solution 1:
If we're doing everything manually with vanilla Python, we can use a for loop to get a running total of the elements of the list at the same time that we use a counter to find the length of the list, and then use those two values to calculate the mean.

### Solution 2:
If we're willing to use a couple of Python's built-in functions (`sum()` and `len()`) then calculating the mean becomes quite straightforward.

### Solution 3:
If we import Python's statistics module we can access a `mean()` function directly. I still have to ask you to wrap it in the outer `mean_list()` function so that I can evaluate your code.

### Solution 4:
If we use NumPy, then throwing the list into a NumPy array gives us access to the `.mean()` method that exists on NumPy arrays

### Solution 5:
Same thing with Pandas, but using the Pandas `Series` object (which leans heavily on NumPy arrays behind the scenes).

What other creative ways were you able to calculate the mean of a list?


Write a function that calculates the mean (average) of a list of numbers.

Mean of a numeric list in Python - Code Challenge

Mean of a List

There are many ways to solve this challenge successfully.

The main consideration is that when the passed-in list contains an even number of elements the operation should sort the list and then find the middle two numbers **and return the _average_ of those two numbers**.

When the passed-in list contains an odd number of elements, the function should sort the list and simply return the middle number.

Write a function that calculates the median of a list of numbers.

Median of a List in Python - Code Challenge

Median of a List

### Solution 1 
Solution 1 contains a verbose yet (hopefully) highly readable vanilla python implementation of the sample variance.

### Solution 2 
Uses NumPy arrays to eliminate the for loop and results in a calculation that is more similar to the mathematical equation provided above

### Solution 3 
Uses the `.var()` method of a pandas Series. Pandas Series objects always calculate the *sample* variance by default.

### Solution 4
We can use the `.var()` method of a NumPy array to the same effect, but NumPy arrays calculate the *population* variance by default so an extra parameter `ddof=1` is required to indicate that we are interested in the *sample* variance.

Write a function that calculates the *sample* variance of a list of numbers.

Sample Variance of a list in Python - Code Challenge

Variance of a List

### Solution 1 
Solution 1 contains a verbose yet (hopefully) highly readable vanilla Python implementation of the sample standard deviation.

### Solution 2
Solution 2 relies on one of the `var_list` function solutions that we wrote in the [Variance of a List](https://temzee.com/code-challenges/variance-of-a-list-python) code challenge as a helper function. Our standard deviation function returns the square root of the value returned by the `var_list` function. To take the square root we are raise the result to the `1/2` power.

### Solution 3
Uses NumPy arrays to eliminate the for loop and results in a calculation that reads more like mathematical equation.

### Solution 4
Uses the `.std()` method of a Pandas Series. Pandas Series objects always calculate the *sample* standard deviation by default.

### Solution 5
We can use the `.std()` method of a NumPy array to the same effect, but NumPy arrays calculate the *population* standard deviation by default so an extra parameter `ddof=1` is required to indicate that we are interested in the *sample* standard deviation.

Write a function that calculates the *sample* Standard Deviation of a list of numbers.

Sample Standard Deviation in Python - Code Challenge

Standard Deviation of a List

### Solution 1
In Solution 1 we calculate the sample size and the mean of the two passed-in lists (`x` and `y`). Then, in a for loop, we calculate the deviation of each observation from its respective mean and multiply those deviations against each other. We use a running total to sum up all of these individual product deviations. This results in the `sum_of_product_deviations` which we then divide by `n-1` to find (and return) the desired covariance.

### Solution 2
In Solution 2 we use two Pandas Series objects and the built-in `.cov()` method to find the covariance between these two Series. We could have reversed the positions of `x` within the return statement found the same result.

### Solution 3
In Solution 3 we used `np.cov()` to find the covariance matrix. We then select from the covariance matrix the particular covariance value that we are interested in.

Try your hand at calculating the sample covariance between two random variables (lists of integers).

Sample Covariance Python Code Challenge

Sample Covariance

### Solution 1
In Solution 1 we calculate the sample covariance and two sample standard deviations separately –using helper functions–and then we put them together to calculate the correlation coefficient.

### Solution 2
In Solution 2 we use two Pandas Series objects and the built-in .corr() method to find the covariance between these two Series. We could have reversed the positions of x within the return statement found the same result.

### Solution 3
In Solution 3 we used np.corrcoef() to find the correlation matrix. We then select from the correlation matrix the particular covariance value that we are interested in.

Write a function to calculate the sample correlation coefficient (r). This task will be very approachable if you have already completed the Standard Deviation and Covariance code challenges.

Correlation Coefficient Python Code Challenge

Correlation Coefficient

Demonstrate that you can calculate the correct slope and intercept coefficient using a simple linear regression model in Python.

Simple Linear Regression Code Challenge in Python

Simple Linear Regression

Use Python (or NumPy if you really *have* to) to calculate the dot product of two vectors represented as Python Lists.

Vector Dot Product Code Challenge

Vector Dot Product

Can you write a function that will generate a matrix (2D Python List or NumPy Array) of integers - with an indicated dimensionality? We'll tell you the number of rows and columns that the matrix should have, you do the rest.

Code Challenges

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