reshape a list?
Robert Kern
robert.kern at gmail.com
Mon Mar 6 21:50:37 CET 2006
KraftDiner wrote:
> I have a list that starts out as a two dimensional list
> I convert it to a 1D list by:
>
> b = sum(a, [])
>
> any idea how I can take be and convert it back to a 2D list?
Alternatively, you could use real multidimensional arrays instead of faking it
with lists.
http://numeric.scipy.org
In [15]: import numpy
In [16]: tmp = numpy.arange(256)**2
In [17]: a = numpy.column_stack((a,)*256)
In [18]: a[:10,:10]
Out[18]:
array([[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
[ 4, 4, 4, 4, 4, 4, 4, 4, 4, 4],
[ 9, 9, 9, 9, 9, 9, 9, 9, 9, 9],
[16, 16, 16, 16, 16, 16, 16, 16, 16, 16],
[25, 25, 25, 25, 25, 25, 25, 25, 25, 25],
[36, 36, 36, 36, 36, 36, 36, 36, 36, 36],
[49, 49, 49, 49, 49, 49, 49, 49, 49, 49],
[64, 64, 64, 64, 64, 64, 64, 64, 64, 64],
[81, 81, 81, 81, 81, 81, 81, 81, 81, 81]])
In [19]: a.shape
Out[19]: (256, 256)
In [20]: a.ravel()[:100]
Out[20]:
array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0])
In [21]: a.ravel().shape
Out[21]: (65536,)
In [22]: b = numpy.reshape(a.ravel(), (256,256))
In [23]: b.shape
Out[23]: (256, 256)
In [24]: (a == b).all()
Out[24]: True
--
Robert Kern
robert.kern at gmail.com
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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