Extra Challenges

A collection of challenges that have been either removed from or not (yet) added to the main lesson.

Looping Over DataFrame

(Please refer to lesson 06-loops-and-functions.md)

The file surveys.csv in the data folder contains 25 years of data from surveys, starting from 1977. We can extract data corresponding to each year in this DataFrame to individual CSV files, by using a for loop:

import pandas as pd

# Load the data into a DataFrame
surveys_df = pd.read_csv('data/surveys.csv')

# Loop through a sequence of years and export selected data
start_year = 1977
end_year = 2002
for year in range(start_year, end_year+1):

    # Select data for the year
    surveys_year = surveys_df[surveys_df.year == year]  

    # Write the new DataFrame to a CSV file
    filename = 'data/surveys' + str(year) + '.csv' 
    surveys_year.to_csv(filename)

What happens if there is no data for a year in a sequence? For example, imagine we used 1976 as the start_year

Solution

We get the expected files for all years between 1977 and 2002, plus an empty data/surveys1976.csv file with only the headers.