numpy的：语法/成语投（N，）阵列为（N，1）阵列？ [英] numpy: syntax/idiom to cast (n,) array to a (n, 1) array?

问题描述

我想投numpy的 ndarray 形状的物体（的 N 的，）到具有一个形状（ N ，1）。我拿出最好的是推出自己的_to_col功能：

I'd like to cast a numpy ndarray object of shape (n,) into one having shape (n, 1). The best I've come up with is to roll my own _to_col function:

def _to_col(a):
    return a.reshape((a.size, 1))

但是，我很难相信这样一个无处不在的操作是不是已经内置到numpy的语法。我想，我只是一直没能想出正确的谷歌搜索找到它。

But it is hard for me to believe that such a ubiquitous operation is not already built into numpy's syntax. I figure that I just have not been able to hit upon the right Google search to find it.

推荐答案

我会用以下内容：

a[:,np.newaxis]

这是另一种（但也许稍微不太清楚）的方式来写同样的事情是：

An alternative (but perhaps slightly less clear) way to write the same thing is:

a[:,None]

以上所有的（包括你的版本）恒定时操作。

All of the above (including your version) are constant-time operations.

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