How to remove duplicate rows in a matrix by considering the repeated values in a specific column?

%% consider the following example.

A = [1 2 4; 3 5 7;1 5 8; 2 9 4]

In matrix A, column 1 has a duplicate value which is 1. I need to keep the first met value and remove the rest accordingly. At the same time, the indices of non-duplicates should not be changed.

The possible solution should be,

A_without_dup = [1 2 4;3 5 7;2 9 4]

%% only the final row is removed because a duplicate is found in that row based on the value of column 1 in A.

Thanks.

Answer 1

[Mohammad Sami]

You can use the unique function to return you the index of the unique values in the first column.

Use the stable keyword so the order is preserved. You can then use the index to keep the unique rows.

[~,uidx] = unique(A(:,1),'stable');
A_without_dup = A(uidx,:);

[Gayan Lankeshwara]

Hi Sami,

Thank you for the answer. It works.

[David Linsenbardt]

You can also combine rows w/ stable and remove rows where duplicates exist in multiple columns:

[~,uidx] = unique(data(:,[1 2]),'rows','stable');

data = data(uidx,:);

[Zach Williams]

David, thank you for also sharing your simplified solution!