[SciPy-user] Slicing arrays
Tom Denniston
tom.denniston at alum.dartmouth.org
Mon Dec 10 15:49:12 EST 2007
Something like this should work:
In [8]: a1 = numpy.ones(100)
In [9]: a1[::3]=3
In [11]: numpy.cumsum(a1)-2
array([ 1., 2., 3., 6., 7., 8., 11., 12., 13.,
16., 17., 18., 21., 22., 23., 26., 27., 28.,
31., 32., 33., 36., 37., 38., 41., 42., 43.,
46., 47., 48., 51., 52., 53., 56., 57., 58.,
61., 62., 63., 66., 67., 68., 71., 72., 73.,
76., 77., 78., 81., 82., 83., 86., 87., 88.,
91., 92., 93., 96., 97., 98., 101., 102., 103.,
106., 107., 108., 111., 112., 113., 116., 117., 118.,
121., 122., 123., 126., 127., 128., 131., 132., 133.,
136., 137., 138., 141., 142., 143., 146., 147., 148.,
151., 152., 153., 156., 157., 158., 161., 162., 163., 166.])
On 12/10/07, Nils Wagner <nwagner at iam.uni-stuttgart.de> wrote:
> Hi all,
>
> I have an array
>
> >>> a
> array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
> 13, 14, 15, 16,
> 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
> 29, 30, 31, 32, 33,
> 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45,
> 46, 47, 48, 49, 50,
> 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62,
> 63, 64, 65])
>
> How can I extract an array b from a such that
>
> >>> b
> array([ 0, 1, 2, 6, 7, 8, 12, 13, 14, 18, 19, 20, 24,
> 25, 26, 30, 31,
> 32, 36, 37, 38, 42, 43, 44, 48, 49, 50, 54, 55,
> 56, 60, 61, 62])
>
> Nils
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