[Numpy-discussion] subsampling
Charles G Waldman
cgw at alum.mit.edu
Thu Feb 14 18:43:01 CST 2002
Mathew Yeates writes:
> how can I take a matrix and subsample it down to
> an arbitrary size? It seems that using slices is
> limited to constant integer step sizes while, if
> I'm converting between arbitrary sizes, I would like
> to subsample at a nonuniform rate.
I'm not sure exactly what you're trying to do, but maybe the following
Python session will show you the way.
>>> from Numeric import *
>>> take.__doc__
'take(a, indices, axis=0). Selects the elements in indices from array a along t he given axis.'
>>> a = fromfunction(lambda i,j: 10*i+j, (10,5))
>>> a
array([[ 0, 1, 2, 3, 4],
[10, 11, 12, 13, 14],
[20, 21, 22, 23, 24],
[30, 31, 32, 33, 34],
[40, 41, 42, 43, 44],
[50, 51, 52, 53, 54],
[60, 61, 62, 63, 64],
[70, 71, 72, 73, 74],
[80, 81, 82, 83, 84],
[90, 91, 92, 93, 94]])
>>> b = take(a,(0,2,3,5,7))
>>> b
array([[ 0, 1, 2, 3, 4],
[20, 21, 22, 23, 24],
[30, 31, 32, 33, 34],
[50, 51, 52, 53, 54],
[70, 71, 72, 73, 74]])
>>> c = take(b,(0,2,3), 1)
>>> c
array([[ 0, 2, 3],
[20, 22, 23],
[30, 32, 33],
[50, 52, 53],
[70, 72, 73]])
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