如何删除numpy数组中的列? [英] How to remove a column in a numpy array?

问题描述

想象一下，我们有一个5x4的矩阵. 我们只需要删除第一个维度. 如何使用 numpy 做到这一点?

Imagine we have a 5x4 matrix. We need to remove only the first dimension. How can we do it with numpy?

array([[  0.,   1.,   2.,   3.],
       [  4.,   5.,   6.,   7.],
       [  8.,   9.,  10.,  11.],
       [ 12.,  13.,  14.,  15.],
       [ 16.,  17.,  18.,  19.]], dtype=float32)

我尝试过:

arr = np.arange(20, dtype=np.float32)
matrix = arr.reshape(5, 4)
new_arr = numpy.delete(matrix, matrix[:,0])
trimmed_matrix = new_arr.reshape(5, 3)

看起来有点笨拙. 我做得对吗? 如果是，是否有更干净的方法来移除尺寸而无需重新塑形?

It looks a bit clunky. Am I doing it correctly? If yes, is there a cleaner way to remove the dimension without reshaping?

推荐答案

如果要从2D Numpy数组中删除列，则可以指定这样的列

If you want to remove a column from a 2D Numpy array you can specify the columns like this

保留所有行并删除第0列(或从第1列开始直到结尾)

to keep all rows and to get rid of column 0 (or start at column 1 through the end)

a[:,1:]

另一种方式，您可以指定要保留的列(并根据需要更改顺序) 这将保留所有行，并且仅使用列0、2、3

another way you can specify the columns you want to keep ( and change the order if you wish) This keeps all rows and only uses columns 0,2,3

a[:,[0,2,3]]

有关此文档，可在此处

如果您想要专门删除列的内容，可以执行以下操作:

And if you want something which specifically removes columns you can do something like this:

idxs = list.range(4)
idxs.pop(2) #this removes elements from the list
a[:, idxs]

和@hpaulj调出numpy.delete()

and @hpaulj brought up numpy.delete()

这将是如何返回沿轴= 1移除2列(0和2)的"a"视图的方法.

This would be how to return a view of 'a' with 2 columns removed (0 and 2) along axis=1.

np.delete(a,[0,2],1)

这实际上并没有从'a'中删除项目，它的返回值是一个新的numpy数组.

This doesn't actually remove the items from 'a', it's return value is a new numpy array.

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