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]使我得到数组的 ith 行(例如[1, 2]).如何访问 ith 列? (例如[1, 3, 5]).而且，这会是一项昂贵的操作吗?

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?

推荐答案

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

类似地，

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

让您访问行. NumPy参考的第1.4节(索引)中对此进行了介绍. .至少从我的经验来看，这是快速的.当然，这比循环访问每个元素要快得多.

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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