30-seconds-of-code/snippets/group_by.md

title, tags

title	tags
group_by	list,object,beginner

Groups the elements of a list based on the given function.

Use list() in combination with map() and fn to map the values of the list to the keys of an object. Use list comprehension to map each element to the appropriate key.

def group_by(lst, fn):
  groups = {}
  for key in list(map(fn,lst)):
    groups[key] = [item for item in lst if fn(item) == key]
  return groups

import math
group_by([6.1, 4.2, 6.3], math.floor); # {4: [4.2], 6: [6.1, 6.3]}
group_by(['one', 'two', 'three'], 'length'); # {3: ['one', 'two'], 5: ['three']}