Remove duplicate rows based on subset of row elements

Hello everyone,

I tried to find a similar problem - relatively simple I believe - but I could not find a solution. If, for instrance, I have a matrix such as

A = [1 1 1 100; 2 2 2 200; 3 3 3 300; 1 1 1 500]

how can I remove from A the fourth row based on the fact that only the thee first elements of the that row are identical to the three elmenets in the first row?

Also, what if I have

A = [1 1 1 100; 2 2 2 200; 3 3 3 300; 1 1 1 500; 1 1 1 600]

and, again, I just want to keep the first row?

Thank you for your help.

Answer 1

[madhan ravi]

A(unique(A(1:3),'rows'),:)

[madhan ravi]

indices_to_be_removed = setdiff(1:size(A,1),unique(A(1:3),'rows'));
A(indices_to_be_removed,:) = []

[Federico Maglione]

Thank you very much for your answer.

A(unique(A(1:3),'rows'),:)

works for the example I gave.

However it does not work if

A = [1 2 3 100; 4 5 6 200; 7 8 9 300; 1 2 3 500];

Could you still help me in this case (again want to remove the last row)?

Thank you

[madhan ravi]

Ah my bad typo:

[~,idx,~] = unique(A(:,1:3),'rows');
A(idx,:)

[Federico Maglione]

Thank you! It works perfectly

[Vijay]

Simple, but an excellent solution.