在Python中从矩阵中选择列向量 [英] Selecting a column vector from a matrix in Python

问题描述

我想在Python/numpy的矩阵中为列向量建立索引，并将其作为列向量而不是一维数组返回.

I would like to index a column vector in a matrix in Python/numpy and have it returned as a column vector and not a 1D array.

x = np.array([[1,2],[3,4]])
x[:,1]
>array([2, 4])

给予

np.transpose(x[:,1])

不是解决方案.根据numpy.transpose文档，这将返回行向量(一维数组).

is not a solution. Following the numpy.transpose documentation, this will return a row vector (1-D array).

推荐答案

少量选项-

x[:,[1]]
x[:,None,1]
x[:,1,None]
x[:,1][:,None]
x[:,1].reshape(-1,1)
x[None,:,1].T

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