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

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]

Do you ONLY want the duplicated 250's removed, or ALL of the duplicated values removed (Like the duped 1173 as well)?

[Khanh]

Thanks for your reply. Just value 250

Answer 1

[Matt]

Khanh,

Try something like this. . .

ind250 = x(:,1) == 250;
if numel(ind250)>1
  x(ind250(2:end),:) = [];
end

[Andrew Reibold]

I think she needs it to work for all duplicates (like 1173 also), not just 250

[Khanh]

Thanks all of you. Matt'answer is the best I want. It works great.

Answer 2

[C.J. Harris]

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]

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]

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.

Answer 3

[Andrew Reibold]

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