# [Numpy-discussion] Slices from an index list

Wed Apr 11 08:15:29 CDT 2012

```On 11/04/2012 14:19, Zachary Pincus wrote:
>> 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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