Get adjacent array value if condition met

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Vineet Guru 2013-5-22

0
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https://ww2.mathworks.cn/matlabcentral/answers/76625-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