Groups the elements of a list based on the given function and returns the count of elements in each group.
- Use
collections.defaultdict
to initialize a dictionary. - Use
map()
to map the values of the given list using the given function. - Iterate over the map and increase the element count each time it occurs.
from collections import defaultdict def count_by(lst, fn = lambda x: x): count = defaultdict(int) for val in map(fn, lst): count[val] += 1 return dict(count)
Examples
from math import floor count_by([6.1, 4.2, 6.3], floor) # {6: 2, 4: 1} count_by(['one', 'two', 'three'], len) # {3: 2, 5: 1}
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