# Reorder Matrix Rows from the row with the most nonzero elements to the row with the least nonzero elements

3 views (last 30 days)
Vance Blake on 5 Jan 2021
Commented: Stephen23 on 5 Jan 2021
I have a matrix with rows of values. I want to order the rows of the matrix so that the matrix with the most nonzero elements is the first row and the next most nonzero elements is the second row, and so on until the end. If two or rows are the same length it doesnt matter which one comes first. Here is the matrix, thanks in advance.
A = [0 1 2 4 7 12 17 22 27 33 42
0 0 1 3 6 11 16 21 26 34 43
0 1 2 4 7 12 17 22 28 35 44
0 0 1 2 8 13 18 23 29 36 45
0 0 1 3 9 14 19 24 30 37 46
0 1 2 5 10 15 20 25 31 38 47
0 1 3 6 11 16 21 26 32 39 48
1 2 4 7 12 17 22 27 33 40 49
0 1 2 5 10 15 20 25 31 41 50];
Stephen23 on 5 Jan 2021

Cris LaPierre on 5 Jan 2021
I'm not aware of anyway to do this without having to write some code, which is probably the exact reason you were given the assignment. Look into logical indexing and sortrows.
##### 3 CommentsShow 1 older commentHide 1 older comment
Cris LaPierre on 5 Jan 2021
Sorry, I meant logical arrays, not logical indexing.
Vance Blake on 5 Jan 2021
Edited: Vance Blake on 5 Jan 2021
This isnt a hw assignment, I'm working on independnet research. I know not to ask hw questions on here. But I was trying to do something like this, but I don't know how to reorder the matrix based on the variable test. Also, I'm not trying to change the order of the nonzero elements in each row; wouldn't sorting them do that ?
test = size(A,2) - sum(A==0, 2);

Stephen23 on 5 Jan 2021
A = [...
0 1 2 4 7 12 17 22 27 33 42
0 0 1 3 6 11 16 21 26 34 43
0 1 2 4 7 12 17 22 28 35 44
0 0 1 2 8 13 18 23 29 36 45
0 0 1 3 9 14 19 24 30 37 46
0 1 2 5 10 15 20 25 31 38 47
0 1 3 6 11 16 21 26 32 39 48
1 2 4 7 12 17 22 27 33 40 49
0 1 2 5 10 15 20 25 31 41 50];
[~,X] = sort(sum(A==0,2));
B = A(X,:)
B = 9×11
1 2 4 7 12 17 22 27 33 40 49 0 1 2 4 7 12 17 22 27 33 42 0 1 2 4 7 12 17 22 28 35 44 0 1 2 5 10 15 20 25 31 38 47 0 1 3 6 11 16 21 26 32 39 48 0 1 2 5 10 15 20 25 31 41 50 0 0 1 3 6 11 16 21 26 34 43 0 0 1 2 8 13 18 23 29 36 45 0 0 1 3 9 14 19 24 30 37 46

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