# Keeping track of order of rows when sorting a matrix

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Aleem Andrew on 8 Nov 2021
Edited: Stephen23 on 8 Nov 2021
I am trying to sort the matrix B below and also keep track of the order in which rows get swapped.
B = [100000001
010000100
001010010
010001100
001000010
000001100
100100000
001010000];
B = -sortrows(-B);
To keep track of each row number, can you for example add the row number column at the beginning, then sort the matrix according to all columns except the first? I am not sure how, because sortrows considers all columns. Or other than this is there any better method?
B = [1100000001
2010000100
3001010010
4010001100
5001000010
6000001100
7100100000
8001010000];
B = -sortrows(-B);

Stephen23 on 8 Nov 2021
Edited: Stephen23 on 8 Nov 2021
"Or other than this is there any better method? "
The MATLAB approach is to get the second output from SORTROWS, which is the sort index, e.g.:
[B,X] = sortrows(-B);
B = -B;
which could be simplified using SORTROWS optional direction argument:
[B,X] = sortrows(B,'descend');
"I am not sure how, because sortrows considers all columns."
Did you read the SORTROWS help? It explains the options that let you select which columns you want to sort by.
Reading the documentation is the best way to learn what MATLAB functions can do.