Selecting only columns of a numpy array where value of a specific row < x

Question

I have a numpy array similar to following structure:

my_array = numpy.array([[1,1,1,2,2,2,3,3,3],  
                  [1,2,3,1,2,3,1,2,3],
                  [1,1,32,4,15,63,763,23,0],
                  [1,1,2,3,1,2,3,1,1],
                  [1,1,1,1,1,1,1,1,1]])

Now I'd like to get subset this array to get only those columns where the value in the 3rd row is < 15.

I can get a boolean list of that as:

list(my_array[2,:]>15)

However I cannot use that boolean list for indexing like:

my_array[:,list(my_array[2,:]>15)]

Probably I have to transform that list to a list of indices and use that to subset the array, but maybe there is an in-built function or straight forward way for selecting the specific columns of the array?

kennytm · Accepted Answer · 2016-09-15 08:02:14Z

1

You should not call list(). The input to [...] are supposed to be numpy arrays.

>>> my_array[:, my_array[2,:]>15]
array([[  1,   2,   3,   3],
       [  3,   3,   1,   2],
       [ 32,  63, 763,  23],
       [  2,   2,   3,   1],
       [  1,   1,   1,   1]])

answered Sep 15, 2016 at 8:02

kennytm

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