使用1d布爾陣列的FIlter 2d陣列

Question

我有兩個numpy數組。其中y相應元素的

x = [[1,2], [3,4], [5,6]] 
y = [True, False, True] 

我想獲得的X元素是True：

filtered_x = filter(x,y) 
print(filtered_x) # [[1,2], [5,6]] should be shown. 

我試過np.extract，但它似乎只工作時x是一維數組。我如何提取x對應的值y的元素是True？

Answer 1

只需使用boolean indexing：

>>> import numpy as np 

>>> x = np.array([[1,2], [3,4], [5,6]]) 
>>> y = np.array([True, False, True]) 
>>> x[y] # or "x[y, :]" because the boolean array is applied to the first dimension (in this case the "rows") 
array([[1, 2], 
     [5, 6]]) 

而如果你想它適用於列，而不是行：

>>> x = np.array([[1,2], [3,4], [5,6]]) 
>>> y = np.array([True, False]) 
>>> x[:, y] # boolean array is applied to the second dimension (in this case the "columns") 
array([[1], 
     [3], 
     [5]]) 

Answer 2

l=[x[i] for i in range(0,len(y)) if y[i]]這將做到這一點。