# Delete rows that have the first same value and keep one row in matrix with 2 colums?

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Khanh on 20 Nov 2014
Edited: Khanh on 23 Nov 2014
Hi everyone,
I have an array:
x=[0,0 ; 250,1050 ; 250,1051 ; 1173,3050 ; 1173 3150].
I don't know how to delete the rows that has the first value is 250 and just keep one.
The row may be (250,1050) or (250,1051), whatever but just one row.
Could someone please suggest me how to do it?
Many thanks.
Andrew Reibold on 20 Nov 2014
Do you ONLY want the duplicated 250's removed, or ALL of the duplicated values removed (Like the duped 1173 as well)?
Khanh on 20 Nov 2014

Matt on 20 Nov 2014
Edited: Matt on 20 Nov 2014
Khanh,
Try something like this. . .
ind250 = x(:,1) == 250;
if numel(ind250)>1
x(ind250(2:end),:) = [];
end
Andrew Reibold on 20 Nov 2014
I think she needs it to work for all duplicates (like 1173 also), not just 250
Khanh on 21 Nov 2014
Edited: Khanh on 21 Nov 2014
Thanks all of you. Matt'answer is the best I want. It works great.

C.J. Harris on 20 Nov 2014
Do you mean something like this?
x = [0,0 ; 250,1050 ; 250,1051 ; 1173,3050 ; 1173 3150];
[~,idx] = unique(x(:,1));
out = x(idx,:)
out =
0 0
250 1051
1173 3150
Matt on 20 Nov 2014
Note that the unique will remove all non-unique values, not just the ones with 250 in the first column. Still, if this is the goal, than this is a much better solution than removing elements one by one
Khanh on 23 Nov 2014
Edited: Khanh on 23 Nov 2014
The result from this code is
out = [0 0;250 1051;1173 3150]
Can I ask you a question? How can I get the result with 1051 (not 1050 )?
Thanks.

Andrew Reibold on 20 Nov 2014
Edited: Andrew Reibold on 20 Nov 2014
This removes any rows where the value in the first column has already been used.
[~,idx] = unique(x(:,1)); %which rows have a unique first value?
x = x(idx,:) %only use those
Output:
x =
0 0
250 1050
1173 3050