切片numpy数组与所需行的列表

Question

我有一个numpy 2d数组A和一个行号列表row_set.我如何获得新的数组B,如if row_set = [0, 2, 5],那么B = [A_row[0], A_row[2], A_row[5]]？

我想到了这样的事情:

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

但我不知道,我怎么能得到一个row_num.

Answer 1

用途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]])

Answer 2

您可以将列表或数组作为索引传递给任何np数组.

>>> r = np.random.randint(0,10,(5,5))
>>> r
array([[3, 8, 9, 8, 4],
       [4, 1, 5, 9, 1],
       [3, 6, 8, 8, 0],
       [5, 1, 7, 6, 1],
       [6, 1, 7, 7, 7]])
>>> idx = [0,3,1]
>>> r[idx]
array([[3, 8, 9, 8, 4],
       [5, 1, 7, 6, 1],
       [4, 1, 5, 9, 1]])