Modifying every alternate element of a sequence
Roberto.Bonvallet at cern.ch
Tue Nov 28 13:14:31 CET 2006
jm.suresh at no.spam.gmail.com wrote:
> I have a list of numbers and I want to build another list with every
> second element multiplied by -1.
> But is there any other better way to do this.
I think the best way is the one that uses slices, as somebody suggested
in this thread. This is another (worse) way, just for fun:
>>> from itertools import cycle
>>> input = [1, 2, 3, 4, 5, 6]
>>> wanted = [x * sign for x, sign in zip(input, cycle([1, -1]))]
[1, -2, 3, -4, 5, -6]
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