Copying values of a numpy array into specific location of sparse matrix

Question

So I am trying to copy values from one numpy array into a sparse matrix. The first array looks like this:

results_array = [[  3.00000000e+00   1.00000000e+00   4.00000000e+00   1.00000000e+03]
[  6.00000000e+00   2.00000000e+00   5.00000000e+00   7.00000000e+02]
[  1.60000000e+01   4.00000000e+00   8.00000000e+00   1.00000000e+03]}

The second value (or results_array[i][1]) dictates the column id, the third value (results_array[i][2]) dictates the row id and the fourth value (results_array[i][3]) dictates the value of that row, column pair.

So far what I have is this:

for i in result_array:
sparse_matrix = csc_matrix((i[3],(i[1],i[2])), shape=(14,14))
print "last array", sparse_matrix

The output I get is:

File "C:/Users/Andrew/Google Drive/Uni/Final Year/Research Project/Programming/Mine/First UEA/xl_optim/Runestone 2.py", line 13, in <module>
sparse_matrix = csc_matrix((i[3],(i[1],i[2])), shape=(14,14))
File "C:\Users\Andrew\Anaconda2\lib\site-packages\scipy\sparse\compressed.py", line 48, in __init__
other = self.__class__(coo_matrix(arg1, shape=shape))
File "C:\Users\###\Anaconda2\lib\site-packages\scipy\sparse\coo.py", line 182, in __init__
self._check()
File "C:\Users\###\Anaconda2\lib\site-packages\scipy\sparse\coo.py", line 219, in _check
nnz = self.nnz
File "C:\Users\###\Anaconda2\lib\site-packages\scipy\sparse\coo.py", line 194, in getnnz
nnz = len(self.data)
TypeError: len() of unsized object

I think I need to create the sparse matrix first and then add the values to it iteratively (I'm imagining something like a .append but to a specific location in the matrix) but I have no idea how to create an empty sparse matrix and then assign values to it.

Let me know if you need further clarification. Thanks!

ali_m · Accepted Answer · 2016-05-13 20:44:19Z

4

The first element in the tuple you pass to csc_matrix needs to be a vector of values, whereas you are passing it an integer. More fundamentally, you're trying to call the csc_matrix constructor multiple times in a loop so that it would overwrite sparse_matrix on each iteration.

You want to call csc_matrix once with a vector for each parameter, like this:

values = results_array[:, 3]
row_idx = results_array[:, 2]
col_idx = results_array[:, 1]

sparse_array = csc_matrix((values, (row_idx, col_idx)), shape=(14, 14))

answered May 13, 2016 at 20:44

ali_m

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