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The map, filter, and reduce functions

Other functions that you might find useful with data structures are map, filter, and reduce. These are very useful in conjunction with other functions, such as lambdas.

map runs given functions on every element of the iterable, returning a generator:

>>> data1, data2 = (1, 2, 3, 4, 5), ('A', 'B', 'C', 'D', 'E')>>> list(map(lambda x: x**2, data1))  # converting to list in order to seE results[1, 4, 9, 16, 25]>>> list(map(lambda x: x.lower(), data2))['a', 'b', 'c', 'd', 'e']

Similarly, filter returns a subarray of elements for which the function returns a true or truthy value:

list(filter(lambda x: x > 3, data1))>>> [4, 5]

Finally, reduce—which was moved to the itertools package in Python 3—runs given functions ...