Pythonic way to return list of every nth item in a larger list
>>> lst = list(range(165))
>>> lst[0::10]
[0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160]
Note that this is around 100 times faster than looping and checking a modulus for each element:
$ python -m timeit -s "lst = list(range(1000))" "lst1 = [x for x in lst if x % 10 == 0]"
1000 loops, best of 3: 525 usec per loop
$ python -m timeit -s "lst = list(range(1000))" "lst1 = lst[0::10]"
100000 loops, best of 3: 4.02 usec per loop
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source_list[::10]
is the most obvious, but this doesn't work for any iterable and is not memory efficient for large lists. -
itertools.islice(source_sequence, 0, None, 10)
works for any iterable and is memory-efficient, but probably is not the fastest solution for large list and big step. (source_list[i] for i in xrange(0, len(source_list), 10))
You can use the slice operator like this:
l = [1,2,3,4,5]
l2 = l[::2] # get subsequent 2nd item
Use range(start, end, step)
li = list(range(0, 1000, 10))
[0, 10, 20, 30, 40, 50, 60, 70, 80, 90 ... 990]
Or, if you have a list use slice: From manual: s[i:j:k] slice of s from i to j with step k
yourlist = [0, ... ,10 ...]
sub = yourlist[::10] # same as yourlist[0:100:10]
>>> sub
[0, 10, 20, 30, 40, 50, 60, 70, 80, 90]