03-6-python-grouping.md

Data 3-6: Python - Grouping

We can use for loops, if statements, and dicts to group data.

Example 1: Grouping

from pprint import pprint

cars = [
    {"model": "Yaris", "make": "Toyota", "color": "red"},
    {"model": "Auris", "make": "Toyota", "color": "red"},
    {"model": "Camry", "make": "Toyota", "color": "green"},
    {"model": "Prius", "make": "Toyota", "color": "yellow"},
    {"model": "Civic", "make": "Honda", "color": "red"},
    {"model": "Model 3", "make": "Tesla", "color": "red"}
]

cars_by_make = {}
for car in cars:
    make = car['make']
    if make in cars_by_make:
        cars_by_make[make].append(car)
    else:
        cars_by_make[make] = [car]

pprint(cars_by_make)

This should output:

{'Honda': [{'make': 'Honda', 'model': 'Civic'}],
 'Tesla': [{'make': 'Tesla', 'model': 'Model 3'}],
 'Toyota': [{'make': 'Toyota', 'model': 'Yaris'},
            {'make': 'Toyota', 'model': 'Auris'},
            {'make': 'Toyota', 'model': 'Camry'},
            {'make': 'Toyota', 'model': 'Prius'}]}

Example 2: Grouping and Counting

number_of_cars_by_make = {}
for car in cars:
    make = car['make']
    if make in number_of_cars_by_make:
        number_of_cars_by_make[make] += 1
    else:
        number_of_cars_by_make[make] = 1

pprint(number_of_cars_by_make)

This should output:

{'Honda': 1, 'Tesla': 1, 'Toyota': 4}

A quick sidenote: PANDAS

If you're manipulating tabular data in Python, it may be a good idea to use the Pandas library. This provides an abstraction called a "DataFrame" (you may be familiar with this if you've used other statistical programming languages like R. It is basically just a representation of a spreadsheet table, but in Python.

If you use Python's Pandas library for data manipulation and analysis instead, the code for the above assignment would look like this: https://gist.github.com/AlJohri/59c9762845519f999eb28fe45276f4c1

➡️ Try It

1. Read vegtables.csv into a variable called vegtables.
2. Group vegtables by color as a variable vegtables_by_color.
3. Output vegtables_by_color into a json called vegtables_by_color.json.