python - 提取numpy矩阵的前n列

Question

我有一个这样的数组：

  array([[-0.57098887, -0.4274751 , -0.38459931, -0.58593526],
         [-0.22279713, -0.51723555,  0.82462029,  0.05319973],
         [ 0.67492385, -0.69294472, -0.2531966 ,  0.01403201],
         [ 0.41086611,  0.26374238,  0.32859738, -0.80848795]])

现在我想提取以下内容：

   [-0.57098887, -0.4274751]
   [-0.22279713, -0.51723555]
   [ 0.67492385, -0.69294472]
   [ 0.41086611,  0.26374238]

所以基本上只是前两列..

Answer 1

如果a是你的数组：

In [11]: a[:,:2]
Out[11]: 
array([[-0.57098887, -0.4274751 ],
       [-0.22279713, -0.51723555],
       [ 0.67492385, -0.69294472],
       [ 0.41086611,  0.26374238]])

Answer 2

我知道这是一个很老的问题-

A = [[1, 2, 3],
     [4, 5, 6],
     [7, 8, 9]]

假设您要提取前 2 行和前 3 列

A_NEW = A[0:2, 0:3]
A_NEW = [[1, 2, 3],
         [4, 5, 6]]

理解语法

A_NEW = A[start_index_row : stop_index_row, 
          start_index_column : stop_index_column)]

如果一个人想要第 2 行和第 2 列和第 3 列

A_NEW = A[1:2, 1:3]

参考numpy indexing and slicing文章——Indexing & Slicing