Processing experimental data with repeated values into a Matrix of results

I need to process data out of a measurement. For each X and Y value, I will get a measured Z as a raw data, but then I need to process all the data to get a Matrix of data. That means there will for same X and Y, several values of Z, so the result that goes into the matrix needs to be weighted in according to the several readings. I have seen some dedicated software that has some cropping or collapsing data functions. Any suggestions on how this can be done in Matlab please? Preferably without libraries if possible.