[Numpy-discussion] Find contiguous sequences of booleans in arrays
David Cournapeau
david@ar.media.kyoto-u.ac...
Mon Sep 17 05:33:03 CDT 2007
Kurdt Bane wrote:
> Hi to all,
>
> I've got an 1-D array of bools and I'd like to find the length of the
> first contiguous sequence of True values, starting from position [0]
> of the array.
> (That's equivalent to find the position of the first occurrence of
> False in the array).
One possibility would be to find the first True and then use cumproduct
to get the length, and then create a view with the remaining elements,
recursively. But this may be slow. You may be a bit smarter to get the
index of the first True value for each sub-sequence by multiplying the
array by itself, shifted by one, and using xor. Whether this is pythonic
and clean, I don't know :)
cheers,
David
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