MATLAB: How to output both rho and pvalues of the Corr function when having an iterative loop

correlationfor loopfunctionoutputpvalrho

Hi, I can't seem to get around how to do this. I have 12xm matrix (a1) of which I want to calculate the linear rank correlation rho an pvalues (using Corr function and pearson correlation type) from paired columns vectors, i.e. between 6 rows in each column and the next 6 rows in that column (these are replicate measurements, designated rep1 and rep2, respectively), and I want to iterate that with a for loop for all the m columns in the matrix a1.
I have it working so that it spits out the rho values in a 1xm vector, but I don't know how to get the script to do that also for the p-values associated with each correlation.
this is the script I have:
            results=zeros(1,size(a1,2));
              rep1=a1(1:6,1:size(a1,2));
              rep2=a1(7:12,1:size(a1,2));
                  for repit = 1:size(a1,2);
                    results(repit) =  corr(rep1(:,repit),rep2(:,repit));
                          end
I know that [r,p] = corr(x,y) gives me both the r and p-value, but how do I build this into the iterative loop that I have going so that it does that for each each two column vectors in every columns of the a1 matrix…..?
I hope I am making this clear enough… otherwise, don't bother asking for clarifications.
Thank you.

Best Answer

Fly, you could use a cell array:
 ...
 [r{repit} p{repit}] = corr(rep1(:,repit),rep2(:,repit));
 ...
The results from the first iteration are then accessed via r{1} and p{1}, from the second in r{2}...
If the r- and p-values are scalars, you can also just use simple numeric arrays:
 [r(repit) p(repit)] = corr(rep1(:,repit),rep2(:,repit));
The advantage of cell arrays for non-scalars is that you don't need to worry about matrix dimensions.
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