map() returns an iterator, and will not process elements until you ask it to. Turn it into a list to force all elements to be processed: list(map(self.do_someting,range(10))) or use collections.deque() with the length set to 0 to not produce a list if you don’t need the map output: from collections import deque deque(map(self.do_someting, range(10))) but … Read more
There is a map method in multiprocessing.Pool. That does multiple processes. And if multiple processes aren’t your dish, you can use multiprocessing.dummy which uses threads. import urllib import multiprocessing.dummy p = multiprocessing.dummy.Pool(5) def f(post): return urllib.urlopen(‘http://stackoverflow.com/questions/%u’ % post) print p.map(f, range(3329361, 3329361 + 5))
list(map(cube, range(1, 11))) is equivalent to [cube(1), cube(2), …, cube(10)] While the list returned by list(filter(f, range(2, 25))) is equivalent to result after running result = [] for i in range(2, 25): if f(i): result.append(i) Notice that when using map, the items in the result are values returned by the function cube. In contrast, the … Read more
Either is fine. Pick the one that seems more readable to you. If the calculation naturally decomposes, as this one does, then the multiple maps is probably more readable. Some calculations won’t naturally decompose, in which case you’re stuck at the former. In neither case should you be worrying that one is significantly more performant … Read more
It is no secret that reduce is not among the favored functions of the Pythonistas. Generically, reduce is a left fold on a list It is conceptually easy to write a fold in Python that will fold left or right on a iterable: def fold(func, iterable, initial=None, reverse=False): x=initial if reverse: iterable=reversed(iterable) for e in … Read more
You can with a lambda: map(lambda a: function(a[0], **a[1]), arguments) or you could use a generator expression or list comprehension, depending on what you want: (function(a, **k) for a, k in arguments) [function(a, **k) for a, k in arguments] In Python 2, map() returns a list (so the list comprehension is the equivalent), in Python … Read more
Use the enumerate() function to add indices: map(function, enumerate(a)) Your function will be passed a tuple, with (index, value). In Python 2, you can specify that Python unpack the tuple for you in the function signature: map(lambda (i, el): i * el, enumerate(a)) Note the (i, el) tuple in the lambda argument specification. You can … Read more
This is usually called maplist/3 and is part of the Prolog prologue. Note the different argument order! :- meta_predicate(maplist(2, ?, ?)). maplist(_C_2, [], []). maplist( C_2, [X|Xs], [Y|Ys]) :- call(C_2, X, Y), maplist( C_2, Xs, Ys). The different argument order permits you to easily nest several maplist-goals. ?- maplist(maplist(test),[[1,2],[3,4]],Rss). Rss = [[1,4],[9,16]]. maplist comes in … Read more
Use replace instead of map: >>> s = pd.Series([‘one’,’two’,’three’,’four’]) >>> recodes = {‘one’:’A’, ‘two’:’B’, ‘three’:’C’} >>> s.map(recodes) 0 A 1 B 2 C 3 NaN dtype: object >>> s.replace(recodes) 0 A 1 B 2 C 3 four dtype: object
I had a task that I only knew the length of the array and needed to transform the items. I wanted to do something like this: let arr = new Array(10).map((val,idx) => idx); To quickly create an array like this: [0,1,2,3,4,5,6,7,8,9] But it didn’t work because: (see Jonathan Lonowski’s answer) The solution could be to … Read more