如何访问 NumPy 多维数组的第 i 列? [英] How to access the ith column of a NumPy multidimensional array?

问题描述

假设我有:

test = numpy.array([[1, 2], [3, 4], [5, 6]])

test[i] 获取数组的 ith<​​/em> 行(例如 [1, 2]).如何访问 ith<​​/em> 列?(例如 [1, 3, 5]).此外，这会是一项昂贵的操作吗?

解决方案

>>>测试[:,0]数组([1, 3, 5])

同样，

<预><代码>>>>测试 [1,:]数组([3, 4])

让您访问行.这在 NumPy 参考的第 1.4 节(索引)中有介绍.这很快，至少根据我的经验.这肯定比访问循环中的每个元素要快得多.

Suppose I have:

test = numpy.array([[1, 2], [3, 4], [5, 6]])

test[i] gets me ith line of the array (eg [1, 2]). How can I access the ith column? (eg [1, 3, 5]). Also, would this be an expensive operation?

解决方案

>>> test[:,0]
array([1, 3, 5])

Similarly,

>>> test[1,:]
array([3, 4])

lets you access rows. This is covered in Section 1.4 (Indexing) of the NumPy reference. This is quick, at least in my experience. It's certainly much quicker than accessing each element in a loop.

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