Passing back data with increasing row indices using Sparse Command

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Huck Febbo 2016-3-17

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关闭： MATLAB Answer Bot 2021-8-20

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

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Answer 1

Walter Roberson 2016-3-17

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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