How to transform numpy.matrix or array to scipy sparse matrix

问题:

For SciPy sparse matrix, one can use todense() or toarray() to transform to NumPy matrix or array. What are the functions to do the inverse?

I searched, but got no idea what keywords should be the right hit.

回答1:

You can pass a numpy array or matrix as an argument when initializing a sparse matrix. For a CSR matrix, for example, you can do the following.

>>> import numpy as np >>> from scipy import sparse >>> A = np.array([[1,2,0],[0,0,3],[1,0,4]]) >>> B = np.matrix([[1,2,0],[0,0,3],[1,0,4]])  >>> A array([[1, 2, 0],        [0, 0, 3],        [1, 0, 4]])  >>> sA = sparse.csr_matrix(A)   # Here's the initialization of the sparse matrix. >>> sB = sparse.csr_matrix(B)  >>> sA '         with 5 stored elements in Compressed Sparse Row format>  >>> print sA   (0, 0)        1   (0, 1)        2   (1, 2)        3   (2, 0)        1   (2, 2)        4 

回答2:

There are several sparse matrix classes in scipy.

bsr_matrix(arg1[, shape, dtype, copy, blocksize]) Block Sparse Row matrix
coo_matrix(arg1[, shape, dtype, copy]) A sparse matrix in COOrdinate format.
csc_matrix(arg1[, shape, dtype, copy]) Compressed Sparse Column matrix
csr_matrix(arg1[, shape, dtype, copy]) Compressed Sparse Row matrix
dia_matrix(arg1[, shape, dtype, copy]) Sparse matrix with DIAgonal storage
dok_matrix(arg1[, shape, dtype, copy]) Dictionary Of Keys based sparse matrix.
lil_matrix(arg1[, shape, dtype, copy]) Row-based linked list sparse matrix

Any of them can do the conversion.

import numpy as np from scipy import sparse a=np.array([[1,0,1],[0,0,1]]) b=sparse.csr_matrix(a) print(b)  (0, 0)  1 (0, 2)  1 (1, 2)  1 

See http://docs.scipy.org/doc/scipy/reference/sparse.html#usage-information .

回答3:

As for the inverse, the function is inv(A), but I won't recommend using it, since for huge matrices it is very computationally costly and unstable. Instead, you should use an approximation to the inverse, or if you want to solve Ax = b you don't really need A^-1.

文章来源: How to transform numpy.matrix or array to scipy sparse matrix