numpy的IndexError：数组太多指数与另一个索引矩阵时， [英] numpy IndexError: too many indices for array when indexing matrix with another

问题描述

我有一个矩阵，我创建这样的：

I have a matrix a which I create like this:

>>> a = np.matrix("1 2 3; 4 5 6; 7 8 9; 10 11 12")

我有我创建这样一个矩阵标签：

I have a matrix labels which I create like this:

>>> labels = np.matrix("1;0;1;1")

这是两个基质中的样子：

This is what the two matricies look like:

>>> a
matrix([[ 1,  2,  3],
        [ 4,  5,  6],
        [ 7,  8,  9],
        [10, 11, 12]])
>>> labels
matrix([[1],
        [0],
        [1],
        [1]])

正如你所看到的，当我选择所有列，是没有问题的。

As you can see, when I select all columns, there is no problem

>>> a[labels == 1, :]
matrix([[ 1,  7, 10]])

但是，当我尝试指定一个专栏中，我得到一个错误

But when I try to specify a column I get an error

>>> a[labels == 1, 1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/site-packages/numpy/matrixlib/defmatrix.py", line 305, in     __getitem__
    out = N.ndarray.__getitem__(self, index)
IndexError: too many indices for array
>>>   

有谁知道这是为什么？
我知道有这已经类似的问题，但他们没有解释我的问题不够好，也不是有帮助的回答我。

Does anybody know why this is? I am aware there are similar questions to this already but none of them explain my problem well enough, neither are the answers helpful to me.

推荐答案

由于标签是一个矩阵，当你做标签== 1 您获得相同形状的布尔矩阵。然后做 A [标签== 1：] 将返回您仅与对应的匹配行的第一列。请注意，您的意向得到：

Since labels is a matrix when you do labels==1 you obtain a boolean matrix of the same shape. Then doing a[labels==1, :] will return you only the first column with the lines corresponding to the match. Note that your intention to get:

matrix([[ 1,  2,  3],
        [ 7,  8,  9],
        [10, 11, 12]])

没有达到（你得到只有第一列），尽管它的工作对numpy的＆下; 1.8（如由@seberg指出）。

was not achieved (you got only the first column), even though it worked for NumPy < 1.8 (as pointed out by @seberg).

为了得到你想要的，你可以使用标签的平面视图是什么：

In order to get what you want you can use a flattened view of labels:

a[labels.view(np.ndarray).ravel()==1, :]

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