Filter, Map & Reduce of lists
# [SNIPPET_NAME: Filter, Map & Reduce of lists] # [SNIPPET_CATEGORIES: Python Core] # [SNIPPET_DESCRIPTION: Simple examples to show common features in everyday work with lists] # [SNIPPET_AUTHOR: Benjamin Klueglein <[email protected]>] # [SNIPPET_LICENSE: GPL] numbers = range(1, 20, 1) # Numbers from 1 to 20 ######################### # Filtering of lists: # Pick a amount of items which match a certain condition ######################### # e.g. Get all odd numbers odd_numbers = filter(lambda n: n % 2, numbers) print odd_numbers # prints [1, 3, 5, 7, 9, 11, 13, 15, 17, 19] ######################### ######################### # Mapping of lists: # Apply a function to each item and return the result of each invocation in a list ######################### # Calculate the square of two for each number squared_numbers = map(lambda n: n ** 2, numbers) # Alternate approach: squared_numbers = [n ** 2 for n in numbers] print squared_numbers # prints [1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 361] ######################### ######################### # Reducing of lists # Apply a function of two arguments cumulatively to the items of a sequence, # from left to right, so as to reduce the sequence to a single value. # (Taken from reduce docstring) ######################### # Sum up all numbers sum_of_numbers = reduce(lambda n, m: n + m, numbers) print sum_of_numbers # prints 190 #########################