In Python, we can group the elements of a list based on a given function. This can be useful in many situations, such as when we want to group a list of words by their length or a list of numbers by their parity. In this challenge, you will be asked to write a function that groups the elements of a list based on a given function.
Write a function group_by(lst, fn) that takes a list lst and a function fn as arguments and returns a dictionary where the keys are the results of applying fn to the elements of lst and the values are lists of elements from lst that produce the corresponding key when fn is applied to them.
For example, if we have a list of numbers [6.1, 4.2, 6.3] and we want to group them by their integer part, we can use the floor function from the math module as the grouping function. The expected output would be {4: [4.2], 6: [6.1, 6.3]}.
from collections import defaultdict
def group_by(lst, fn):
d = defaultdict(list)
for el in lst:
d[fn(el)].append(el)
return dict(d)from math import floor
group_by([6.1, 4.2, 6.3], floor) ## {4: [4.2], 6: [6.1, 6.3]}
group_by(['one', 'two', 'three'], len) ## {3: ['one', 'two'], 5: ['three']}In this challenge, you have learned how to group the elements of a list based on a given function. You have also written a function that does this by using a dictionary to store the groups and a loop to populate them. This is a useful technique that can be applied in many different contexts.
