对scipy.sparse.csr_matrix中的行求和

问题描述

我的csr_matrix很大，我想添加行并获得具有相同列数但行数减少的新csr_matrix. (上下文:该矩阵是从sklearn CountVectorizer获得的文档项矩阵，我希望能够根据与这些文档相关的代码快速组合文档)

I have a big csr_matrix and I want to add over rows and obtain a new csr_matrix with the same number of columns but reduced number of rows. (Context: The matrix is a document-term matrix obtained from sklearn CountVectorizer and I want to be able to quickly combine documents according to codes associated with these documents)

举一个最小的例子，这是我的矩阵:

For a minimal example, this is my matrix:

import numpy as np
from scipy.sparse import csr_matrix
from scipy.sparse import vstack

row = np.array([0, 4, 1, 3, 2])
col = np.array([0, 2, 2, 0, 1])
dat = np.array([1, 2, 3, 4, 5])
A = csr_matrix((dat, (row, col)), shape=(5, 5))
print A.toarray()

[[1 0 0 0 0]
 [0 0 3 0 0]
 [0 5 0 0 0]
 [4 0 0 0 0]
 [0 0 2 0 0]]

不能说我想要一个新的矩阵B，其中行(1，4)和(2，3，5)通过求和相结合，看起来像这样:

No let's say I want a new matrix B in which rows (1, 4) and (2, 3, 5) are combined by summing them, which would look something like this:

[[5 0 0 0 0]
 [0 5 5 0 0]]

并且应该再次采用稀疏格式(因为我正在使用的实际数据很大).我试图对矩阵的切片求和，然后将其堆叠:

And should be again in sparse format (because the real data I'm working with is large). I tried to sum over slices of the matrix and then stack it:

idx1 = [1, 4]
idx2 = [2, 3, 5]
A_sub1 = A[idx1, :].sum(axis=1)
A_sub2 = A[idx2, :].sum(axis=1)
B = vstack((A_sub1, A_sub2))

但是这给了我仅用于切片中非零列的求和值，因此我无法将其与其他切片结合使用，因为求和的切片中的列数不同.

But this gives me the summed up values just for the non-zero columns in the slice, so I can't combine it with the other slices because the number of columns in the summed slices are different.

我觉得必须有一个简单的方法来做到这一点.但是我在网上或文档中都找不到对此的任何讨论.我想念什么?

I feel like there must be an easy way to do this. But I couldn't find any discussion of this online or in the documentation. What am I missing?

谢谢您的帮助

推荐答案

请注意，您可以通过仔细构造另一个矩阵来做到这一点.这对于密集矩阵的工作方式如下:

Note that you can do this by carefully constructing another matrix. Here's how it would work for a dense matrix:

>>> S = np.array([[1, 0, 0, 1, 0,], [0, 1, 1, 0, 1]])
>>> np.dot(S, A.toarray())
array([[5, 0, 0, 0, 0],
       [0, 5, 5, 0, 0]])
>>>

稀疏版本仅稍微复杂一点. row:

The sparse version is only a little more complicated. The information about which rows should be summed together is encoded in row:

col = range(5)
row = [0, 1, 1, 0, 1]
dat = [1, 1, 1, 1, 1]
S = csr_matrix((dat, (row, col)), shape=(2, 5))
result = S * A
# check that the result is another sparse matrix
print type(result)
# check that the values are the ones we want
print result.toarray()

输出:

<class 'scipy.sparse.csr.csr_matrix'>
[[5 0 0 0 0]
 [0 5 5 0 0]]

通过在row中包含更高的值并相应地扩展S的形状，可以处理输出中的更多行.

You can handle more rows in your output by including higher values in row and extending the shape of S accordingly.

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