[Numpy-discussion] Summing indices of heterogeneous shapes
Michael Hoffman
b3i4old02@sneakemail....
Tue Apr 22 03:31:22 CDT 2008
Michael Hoffman wrote:
> In the following example I can sum up lists of column indices:
>
> >>> x = numpy.arange(30)
> >>> x.shape = (6, 5)
> >>> x
> 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]])
> >>> cols = [[0, 1], [2, 3]]
> >>> x[:, cols].sum(2)
> array([[ 1, 5],
> [11, 15],
> [21, 25],
> [31, 35],
> [41, 45],
> [51, 55]])
>
> Is there a way to do this if the shapes of the lists are heterogeneous?
> For example, what if I wanted to set cols = [[0, 1], [2, 3], [1, 2, 3]]?
> What's the best way to get a sensible result?
One way I thought of is to add an extra column to x that is full of
zeros, and fill in any smaller lists in cols with that. But this will be
pretty clunky and slow.
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