[Numpy-discussion] Interleaved Arrays and

Robert kxroberto@googlemail....
Tue Jun 16 14:18:02 CDT 2009


Ian Mallett wrote:

> 
> n = #blah
> testlist = []
> for x in xrange(n):
>     for y in xrange(n):
>         testlist.append([x,y])
>         testlist.append([x+1,y])
> 
> If "testlist" is an array (i.e., I could go: "array(testlist)"), it 
> works nicely.  However, my Python method is certainly improveable with 
> numpy.  I suspect the best way is interleaving the arrays [x,y->yn] and 
> [x+1,y->yn] n times, but I couldn't figure out how to do that...
> 


e.g with column_stack

 >>> n = 10
 >>> xx = np.ones(n)
 >>> yy = np.arange(n)
 >>> aa = np.column_stack((xx,yy))
 >>> bb = np.column_stack((xx+1,yy))
 >>> aa
array([[ 1.,  0.],
        [ 1.,  1.],
        [ 1.,  2.],
        [ 1.,  3.],
        [ 1.,  4.],
        [ 1.,  5.],
        [ 1.,  6.],
        [ 1.,  7.],
        [ 1.,  8.],
        [ 1.,  9.]])
 >>> bb
array([[ 2.,  0.],
        [ 2.,  1.],
        [ 2.,  2.],
        [ 2.,  3.],
        [ 2.,  4.],
        [ 2.,  5.],
        [ 2.,  6.],
        [ 2.,  7.],
        [ 2.,  8.],
        [ 2.,  9.]])
 >>> np.column_stack((aa,bb))
array([[ 1.,  0.,  2.,  0.],
        [ 1.,  1.,  2.,  1.],
        [ 1.,  2.,  2.,  2.],
        [ 1.,  3.,  2.,  3.],
        [ 1.,  4.,  2.,  4.],
        [ 1.,  5.,  2.,  5.],
        [ 1.,  6.,  2.,  6.],
        [ 1.,  7.,  2.,  7.],
        [ 1.,  8.,  2.,  8.],
        [ 1.,  9.,  2.,  9.]])
 >>> cc = _
 >>> cc.reshape((n*2,2))
array([[ 1.,  0.],
        [ 2.,  0.],
        [ 1.,  1.],
        [ 2.,  1.],
        [ 1.,  2.],
        [ 2.,  2.],
        [ 1.,  3.],
        [ 2.,  3.],
        [ 1.,  4.],
        [ 2.,  4.],
        [ 1.,  5.],
        [ 2.,  5.],
        [ 1.,  6.],
        [ 2.,  6.],
        [ 1.,  7.],
        [ 2.,  7.],
        [ 1.,  8.],
        [ 2.,  8.],
        [ 1.,  9.],
        [ 2.,  9.]])
 >>>


However I feel too, there is a intuitive abbrev function like 
'interleave' or so missing in numpy shape_base or so.


Robert





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