How can I get one column of a Numpy array?

Question

I am triyng to get the 3 columns of a NumPy (RGB) array:

print px
[[[  0   0   0]
  [255 255 255]
  [255   0   0]
  [  0 255   0]
  [  0   0 255]]]

print px[:,0]
print px[:,1]
print px[:,2]

[[0 0 0]]
[[255 255 255]]
[[255   0   0]]

but I would like to get the R, G and B like

[[0 255 255 0 0]]
[[0 255 0 255 0]]
[[0 255 0 0 255]]

Could you help me?

Thank you

Hugo

Carsten · Accepted Answer · 2014-02-20 14:38:56Z

3

Your array px is three-dimensional: the first dimension has just a single element: the complete arrays containing rows and colums. The second dimension is rows, the third is colums. Therefore, to select a column, and have it embedded in the outermost dimension like you have, use the following:

>>> print px[:,:,0]
[[  0 255 255   0   0]]

>>> print px[:,:,1]
[[  0 255   0 255   0]]

>>> print px[:,:,2]
[[  0 255   0   0 255]]

answered Feb 20, 2014 at 14:38

Carsten

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1 Comment

Hugo Over a year ago

I would like to transform this array into a Pandas Dataframe to use a scatter matrix. Should I use? f = pd.DataFrame(px[:,:,:], columns=['R', 'G', 'B'])

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