Get adjacent array value if condition met

Hi, I have a problem which I have been struggling with for a while and was wondering if some kind soul can help me out.

I have an array of two columns. The values in the first are incrementing integers up to 20 (so 1 to 20 in increasing order). The second column is a set of random integers. So each vlue in cloum 1 is matched with a random integer in column 2. I have called this array H.

What I seek help on is this: I need to create a new array of values in column 1 that match a specific number from cloumn B. So the new array, I call z, holds only those values where its corresponding vlue in column 2 are all the same.

The code I wrote is this:

z= [];

m = 20;

for i=1:1:m

    if H(:,2)== 3    %I would like to create an array 'z' of all values 
                     %in col 1 which has 3 as a corresponding value         
                     % in col 2.

    z = H(:,1);
    z = [z;z];
    end
end

I

[Iain]

Have a look at the "unique" function.

Answer 1

[the cyclist]

z = H(H(:,2)==3,1);

[Vineet Guru]

Brilliant!!! It works. Many thanks. Didn't know why I was tying myself in knots.