How To Build A Matrix One Column At A Time

I am wanting to build some matrices one column at a time, with columns from an existing matrix, as per the code below. # x is an existing matrix, y is an array, pos_classes is a se

Solution 1:

You're going about this the wrong way. It's almost always better to do such things in a vectorized way in numpy.

First, build your index array y_pos_actual. Then, simply do

x_pos = x[:, y_pos_actual]

This will select all columns given by the indices y_pos_actual into a new matrix x_pos. You can do the same row-wise using

x_pos = x[y_pos_actual, :]