Problem

Given a dataframe of stock prices, return a new dataframe with the percent change in stock price for each day.
Input:
| Date       | Stock Price |
|------------|-------------|
| 1/1/2018   | 10          |
| 1/2/2018   | 11          |
| 1/3/2018   | 12          |
Output:
| Date       | Percent Change |
|------------|----------------|
| 1/1/2018   | 0              |
| 1/2/2018   | 0.1            |
| 1/3/2018   | 0.0833333333   |

Solution

import pandas as pd

def percent_change(df):
    df['Percent Change'] = df['Stock Price'].pct_change()
    return df

df = pd.DataFrame({'Date': ['1/1/2018', '1/2/2018', '1/3/2018'], 'Stock Price': [10, 11, 12]})
print(percent_change(df))


The solution is optimal because it uses the built-in pct_change() function in pandas.