RE: [Numpy-discussion] Removing rows and columns of a matrix
Nils Wagner writes:
In any case I am interested in a reliable workaround for this feature.
A small example would be appreciated. Thanks in advance.
Numarray (and Numeric to a certain extent) currently is centered around what rows or columns you want rather than those you don't. Writing a reasonably efficient function to do this in a more convenient way is not hard. Here is an example for numarray (not tested, nor does it have any error checking to ensure the input array has sufficient dimensions or that the index is within the array bounds): def remove(arr, index, dim=0): """Remove subarray at index and dimension specified""" # make selected dimension the first one swparr = swapaxes(arr, 0, dim) indices = range(swparr.shape[0]) del indices[index] newarray = swparr[indices] # reorder axes as they originally appeared. return swapaxes(newarray, 0, dim) Then you can say x = remove(x, 5) to remove the 6th row or x = remove(x, 4, dim=1) to remove the 5th column. (depending on what you call rows or columns; in the examples I'm taking an image-oriented view rather than a matrix-oriented view) Perry
------------------- Nils Wagner writes:
In any case I am interested in a reliable
workaround for this feature.
A small example would be appreciated. Thanks in advance.
Numarray (and Numeric to a certain extent) currently is centered around what rows or columns you want rather than those you don't. Writing a reasonably efficient function to do this in a more convenient way is not hard. Here is an example for numarray (not tested, nor does it have any error checking to ensure the input array has sufficient dimensions or that the index is within the array bounds): def remove(arr, index, dim=0): """Remove subarray at index and dimension specified""" # make selected dimension the first one swparr = swapaxes(arr, 0, dim) indices = range(swparr.shape[0]) del indices[index] newarray = swparr[indices] # reorder axes as they originally appeared. return swapaxes(newarray, 0, dim) Then you can say x = remove(x, 5) to remove the 6th row or x = remove(x, 4, dim=1) to remove the 5th column. (depending on what you call rows or columns; in the examples I'm taking an image-oriented view rather than a matrix-oriented view) Perry Perry, Thank you for your reply. Unfortunately, I am not familiar with numarray. This is the output of my test program. from scipy import * from RandomArray import * from numarray import * def remove(arr, index, dim=0): """Remove subarray at index and dimension specified""" # make selected dimension the first one swparr = swapaxes(arr, 0, dim) indices = range(swparr.shape[0]) del indices[index] newarray = swparr[indices] # reorder axes as they originally appeared. return swapaxes(newarray, 0, dim) #Then you can say a = rand(5,5) print a a = remove(a, 2) print a #to remove the 3th row or #to remove the 3th column a = remove(a, 2, dim=1) print a [[ 0.87329948 0.81829292 0.72929943 0.13012239 0.49291104] [ 0.58665377 0.78030288 0.85906255 0.11409029 0.77719343] [ 0.01325159 0.03389675 0.25417367 0.51117259 0.61979091] [ 0.32406124 0.24500449 0.06147733 0.04323368 0.64497042] [ 0.10133368 0.25028452 0.33645368 0.34395722 0.34052679]] Traceback (most recent call last): File "nils.py", line 19, in ? a = remove(a, 2) File "nils.py", line 8, in remove swparr = swapaxes(arr, 0, dim) File "/usr/lib/python2.2/site-packages/numarray/generic.py", line 855, in swapaxes v = _nc.inputarray(array).view() File "/usr/lib/python2.2/site-packages/numarray/numarraycore.py", line 310, in inputarray return array(seq, type=type, typecode=typecode, copy=0) File "/usr/lib/python2.2/site-packages/numarray/numarraycore.py", line 303, in array raise ValueError("Unknown input type") ValueError: Unknown input type Any idea ? Nils _______________________________________________ SciPy-user mailing list SciPy-user@scipy.net http://www.scipy.net/mailman/listinfo/scipy-user
------------------- Nils Wagner writes:
In any case I am interested in a reliable
workaround for this feature.
A small example would be appreciated. Thanks in advance.
Numarray (and Numeric to a certain extent) currently is centered around what rows or columns you want rather than those you don't. Writing a reasonably efficient function to do this in a more convenient way is not hard. Here is an example for numarray (not tested, nor does it have any error checking to ensure the input array has sufficient dimensions or that the index is within the array bounds): def remove(arr, index, dim=0): """Remove subarray at index and dimension specified""" # make selected dimension the first one swparr = swapaxes(arr, 0, dim) indices = range(swparr.shape[0]) del indices[index] newarray = swparr[indices] # reorder axes as they originally appeared. return swapaxes(newarray, 0, dim) Then you can say x = remove(x, 5) to remove the 6th row or x = remove(x, 4, dim=1) to remove the 5th column. (depending on what you call rows or columns; in the examples I'm taking an image-oriented view rather than a matrix-oriented view) Perry Perry, Thank you for your reply. Unfortunately, I am not familiar with numarray. This is the output of my test program. from scipy import * from RandomArray import * from numarray import * def remove(arr, index, dim=0): """Remove subarray at index and dimension specified""" # make selected dimension the first one swparr = swapaxes(arr, 0, dim) indices = range(swparr.shape[0]) del indices[index] newarray = swparr[indices] # reorder axes as they originally appeared. return swapaxes(newarray, 0, dim) #Then you can say a = rand(5,5) print a a = remove(a, 2) print a #to remove the 3th row or #to remove the 3th column a = remove(a, 2, dim=1) print a [[ 0.87329948 0.81829292 0.72929943 0.13012239 0.49291104] [ 0.58665377 0.78030288 0.85906255 0.11409029 0.77719343] [ 0.01325159 0.03389675 0.25417367 0.51117259 0.61979091] [ 0.32406124 0.24500449 0.06147733 0.04323368 0.64497042] [ 0.10133368 0.25028452 0.33645368 0.34395722 0.34052679]] Traceback (most recent call last): File "nils.py", line 19, in ? a = remove(a, 2) File "nils.py", line 8, in remove swparr = swapaxes(arr, 0, dim) File "/usr/lib/python2.2/site-packages/numarray/generic.py", line 855, in swapaxes v = _nc.inputarray(array).view() File "/usr/lib/python2.2/site-packages/numarray/numarraycore.py", line 310, in inputarray return array(seq, type=type, typecode=typecode, copy=0) File "/usr/lib/python2.2/site-packages/numarray/numarraycore.py", line 303, in array raise ValueError("Unknown input type") ValueError: Unknown input type Any idea ? Nils _______________________________________________ SciPy-user mailing list SciPy-user@scipy.net http://www.scipy.net/mailman/listinfo/scipy-user
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Nils Wagner -
Perry Greenfield