Python: Map Function to List
Map Function to List
map function applies a function to all elements of a list.
map(f, list) → applies function f to all elements in list. Return the new list. (does not modify the original list)
# -*- coding: utf-8 -*- # python def ff(n): return n*n print map(ff, [1,2,3,4]) # [1, 4, 9, 16]
# -*- coding: utf-8 -*- # python def ff(n): return n+1 print map(ff, [1,2,3,4]) # [2, 3, 4, 5]
map(f, list1, list2, list3, …) → applies f to all lists in parallel.
That is, first element of result would be
f(e1,e2,e3) where its args are first elemet of each list. f should take same number args as there are lists. All lists must have same number of elements (if short,
None is used). Return the new list.
# -*- coding: utf-8 -*- # python def ff(x1, x2, x3): return str(x1)+ str(x2) + str(x3) print map(ff, [1, 2, 3], ["a", "b", "c"], [4, 5, 6]) # ['1a4', '2b5', '3c6']
Removing Elements in a List
To remove elements in a list that satisfies some criterion, use the function
filter(f, list). The f will be applied to each element in the list. If
False, then that element will not be in the resulting list.
# -*- coding: utf-8 -*- # python aa = range(11) # list 0 to 10 def ff(n): return n % 2 == 0 # return True if divisible by 2 bb = list(filter( ff, aa)) # python 2, “filter” returns a list # in python 3, “filter” returns iterator object. Use list() to convertt to list. print(bb2) # [0, 2, 4, 6, 8, 10]
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