# How to quickly find the maximum group of same rows in a matrix?

3 views (last 30 days)
Benson Gou on 18 Nov 2019
Commented: Star Strider on 2 Dec 2019
Dear All,
I have a matrix and there exist identical rows in the matrix. I want to find the maximum group of identical rows in this matrix. For example, I have a matrix as follows:
A = [0 1 0 1 0 0 0 0; 1 0 0 0 1 0 0 0; 1 0 0 0 1 0 0 0; 1 1 0 0 0 0 0 0; 0 0 1 0 0 0 0 1; 0 0 0 0 0 1 1 0; 0 1 0 1 0 0 0 0; 0 1 0 1 0 0 0 0].
There are two groups of identical rows: {row 1, row 7 and row 8}, {row 2, row 3}. So the answer is {row 1, row 7, row 8}. But how can I quickly find it?
Best regsards,
Benson

Star Strider on 18 Nov 2019
Try this:
A = [0 1 0 1 0 0 0 0; 1 0 0 0 1 0 0 0; 1 0 0 0 1 0 0 0; 1 1 0 0 0 0 0 0; 0 0 1 0 0 0 0 1; 0 0 0 0 0 1 1 0; 0 1 0 1 0 0 0 0; 0 1 0 1 0 0 0 0];
[Au,~,idx] = unique(A, 'rows');
tally = accumarray(idx, 1);
Out = A(idx == max(tally),:) % The Rows Themselves
RowIdx = find(idx == max(tally)) % The Row Indices
producing:
RowIdx =
1
7
8
Star Strider on 2 Dec 2019
As always, my pleasure!
Happy Holidays to you, too!

### Categories

Find more on Calendar in Help Center and File Exchange

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by