subscript assignment to dataset array

I understand the problem with my code, that chrom{n}(:,k) is a dataset at each level of n. But i do not know how to correctly subscript chrom{n}, to get the data I need to perform the calculation. I could create a new matrix for each n, but I've been scolded about this before so I want to do it properly.

Thanks!

 % calculate number of samples
  file = diagnoseTargetsfalciparumEvolved2;
  [a,b] = size(file);
  totalSamples = b-4;

chrom = cell(16,1);
for n = 1:16;
chrom{n} = file(file.chr==n,:);
end

xbar = zeros(16,1);
for n = 1:16;
    for k = 4:(totalSamples) + 3;
        xbar(n,k-3) = mean(double(chrom{n}(:,k)),1);
    end
end

norm = cell(16,1);
for n = 1:16;
norm{n}(:,1:4) = chrom{n}(:,[1:3,14]);
    for k = 4:(totalSamples) + 3;
        norm{n}(:,k + 1) =chrom{n}(:,k)/(xbar(n,k-3));
    end
end