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I am currently dealing with really huge (~ 80,000 x 80,000) sparse matrices. I this context I need to read the number of non-default values in each row.

When Accessing the i-th row of a SparseArray, this information is given.

E.g.

test = SparseArray[{{1, 1} -> 3, {1, 5} -> 2, {5, 3} -> 1}];

test[[1]]

returns SparseArray[<2>, {5}]

However, I fail to access the number of entries (here 2) to assign it to a variable.

I did not find any information in the documentation so far.

Does anyone have an idea?

Thx

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# Mathematica SparseArray Access Non-Default Values

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