Question

I have a numpy 2d array A, and a list of row numbers row_set. How can I get new array B such as if row_set = [0, 2, 5], then B = [A_row[0], A_row[2], A_row[5]]?

I thought of something like this:

def slice_matrix(A, row_set):
    slice = array([row for row in A if row_num in row_set])

but I don’t have any idea, how can I get a row_num.

Answer 1

Use take():

In [87]: m = np.random.random((6, 2))

In [88]: m
Out[88]: 
array([[ 0.6641412 ,  0.31556053],
       [ 0.11480163,  0.00143887],
       [ 0.4677745 ,  0.43055324],
       [ 0.49749099,  0.15678506],
       [ 0.48024596,  0.65701218],
       [ 0.48952677,  0.97089177]])

In [89]: m.take([0, 2, 5], axis=0)
Out[89]: 
array([[ 0.6641412 ,  0.31556053],
       [ 0.4677745 ,  0.43055324],
       [ 0.48952677,  0.97089177]])