index generation for multidimensional discretization

Hi,

I require to discretize (bin) my feature space X, it has corresponding function values Y, therefore I need the index of the values in the bin.

So I have a very crude which does what I want but it is not that nice to expand for larger dimensions...

X = randn(1000,4,1);
Y = randn(1000,1);

nBins = 2;
[xD,E] = discretize(X,nBins);

idx = cell(nBins,nBins,nBins,nBins);
for i = 1:size(X,1)
    idx{xD(i,1),xD(i,2),xD(i,3),xD(i,4)}(end+1) = i;
end


Y(idx{1,2,1,2},:)

Is there a pre-implemented code which does this (but in nice), or some fancy new algorithm which does bining with indexing (however I have only Matlab 2018 available)?

Kind Regards Max