Grouping similar items

Sometimes you might face a list of entries that has multiple, repeated entries and you might want to group the similar ones based on some kind of property.

For example, here is a list of names:

names = [('Alex', 'Zanardi'),
         ('Julius', 'Caesar'),
         ('Anakin', 'Skywalker'),
         ('Joseph', 'Joestar')]

We might want to build a group of all people whose names start with the same character, so we can keep our phone book in alphabetical order instead of having names randomly scattered here and there.

How to do it...

The itertools module is again a very powerful tool that provides us with the foundations we need to handle iterables:

import itertools

def group_by_key(iterable, key):
    iterable = sorted(iterable, key=key)
    return {k: list(g) for k,g in itertools.groupby(iterable, key)}

Given our list of names, we can apply a key function that grabs the first character of the name so that all entries will be grouped by it:

>>> group_by_key(names, lambda...