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Sort twice solution in Clear category for Sort Array by Element Frequency by Krischtopp
def frequency_sort(items):
items_copy = items[:] # make a copy to prevent the list accessing itself while being sorted, which would lead to undefined behaviour
items.sort(key=lambda item:items_copy.index(item)) # sort items by their first appearance
items.sort(key=lambda item:-items_copy.count(item)) # sort items by their frequency in descending order (the minus make the highest frequency the smallest value)
return items
if __name__ == '__main__':
print("Example:")
print(frequency_sort([4, 6, 2, 2, 6, 4, 4, 4]))
# These "asserts" are used for self-checking and not for an auto-testing
assert list(frequency_sort([4, 6, 2, 2, 6, 4, 4, 4])) == [4, 4, 4, 4, 6, 6, 2, 2]
assert list(frequency_sort(['bob', 'bob', 'carl', 'alex', 'bob'])) == ['bob', 'bob', 'bob', 'carl', 'alex']
assert list(frequency_sort([17, 99, 42])) == [17, 99, 42]
assert list(frequency_sort([])) == []
assert list(frequency_sort([1])) == [1]
print("Coding complete? Click 'Check' to earn cool rewards!")
Feb. 2, 2020
