如何在没有循环的情况下从itertools.combinations创建一个numpy数组

Question

有没有办法让这个结果没有循环？我在W[range(W.shape[0]),的花式索引中做了几次尝试...但迄今为止都不成功。

import itertools 
import numpy as np 
n = 4 
ct = 2 
one_index_tuples = list(itertools.combinations(range(n), r=ct)) 
W = np.zeros((len(one_index_tuples), n), dtype='int') 
for row_index, col_index in enumerate(one_index_tuples): 
    W[row_index, col_index] = 1 
print(W) 

结果：

[[1 1 0 0] 
[1 0 1 0] 
[1 0 0 1] 
[0 1 1 0] 
[0 1 0 1] 
[0 0 1 1]] 

Answer 1

您可以使用花哨的索引（advanced indexing）如下：

# reshape the row index to 2d since your column index is also 2d so that the row index and 
# column index will broadcast properly 
W[np.arange(len(one_index_tuples))[:, None], one_index_tuples] = 1 

W 
#array([[1, 1, 0, 0], 
#  [1, 0, 1, 0], 
#  [1, 0, 0, 1], 
#  [0, 1, 1, 0], 
#  [0, 1, 0, 1], 
#  [0, 0, 1, 1]]) 

Answer 2

试试这个：

[[ 1 if i in x else 0 for i in range(n) ] for x in itertools.combinations(range(n), ct)]