[Numpy-discussion] Slices from an index list

Zachary Pincus zachary.pincus@yale....
Wed Apr 11 07:19:37 CDT 2012


> Here's one way you could do it:
> 
> In [43]: indices = [0,1,2,3,5,7,8,9,10,12,13,14]
> 
> In [44]: jumps = where(diff(indices) != 1)[0] + 1
> 
> In [45]: starts = hstack((0, jumps))
> 
> In [46]: ends = hstack((jumps, len(indices)))
> 
> In [47]: slices = [slice(start, end) for start, end in zip(starts, ends)]
> 
> In [48]: slices
> Out[48]: [slice(0, 4, None), slice(4, 5, None), slice(5, 9, None), slice(9, 12, None)]

If you're only going to use the slices to divide up the list, you could use numpy.split and skip creating the slice objects:

indices = [0,1,2,3,5,7,8,9,10,12,13,14]
jumps = numpy.where(numpy.diff(indices) != 1)[0] + 1
numpy.split(indices, jumps)

giving:
[array([0, 1, 2, 3]), array([5]), array([ 7,  8,  9, 10]), array([12, 13, 14])]

Zach

(btw, Warren, the method to calculate the jumps is cute. I'll have to remember that.)



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