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Passing back data with increasing row indices using Sparse Command

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Huck Febbo
Huck Febbo on 17 Mar 2016
Closed: MATLAB Answer Bot on 20 Aug 2021 at 17:28
By default the sparse command passes back the non-zero elements in a matrix arranged by increasing column indices:
A = [ 0 0 1; 0 0 2; 0 2 1];
B = sparse(A)
B =
(3,2) 2
(1,3) 1
(2,3) 2
(3,3) 1
Is there a way to change this so that it passes back the sparse matrix in increasing row indices? In this case
B =
(1,3) 1
(2,3) 2
(3,2) 2
(3,3) 1

Answers (1)

Walter Roberson
Walter Roberson on 17 Mar 2016
You are confusing the display of B with the content of B. The disp() and display() of sparse matrices is in the order you indicate. However that does not mean that the values are "passed back" in that order, just that they are displayed in that order. (Internally, they are in fact ordered by column, but that is an internal detail.)
You can do this:
[r, c, s] = find(B);
rcs = sort([r,c,s], 2);
fprintf('(%d,%d) %g\n', rcs.'); %the transpose of values is not obvious but it is consistent with the rest of MATLAB

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