Re: Mathematica SparseArray Access Non-Default Values
- To: mathgroup at smc.vnet.net
- Subject: [mg108385] Re: Mathematica SparseArray Access Non-Default Values
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Mon, 15 Mar 2010 07:02:30 -0500 (EST)
- Reply-to: hanlonr at cox.net
test = SparseArray[{
{1, 1} -> 3, {1, 5} -> 2, {5, 3} -> 1}];
Count[ArrayRules[test], {1, _} -> _]
2
Count[ArrayRules[test], {1, _}, 2]
2
Bob Hanlon
---- wima <tba2 at gmx.de> wrote:
=============
Hi,
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