xList <- lapply(1:nCol, function(x) unique(c(x, sample(1:nCol, sample(1:nCol, 1)))))

 xMatrix <- matrix(rnorm(nRow*nCol), nrow = nRow)

################Make a new matrix based on the information of xList
 xMatrixNew <- xMatrix

 for (ii in 1:nRow){
   xRow <- xMatrix[ii, ]
   for (jj in 1:nCol){
     xMatrixNew[ii, jj] <- xMatrix[ii, jj]*sum(xRow[xList[[jj]]])/sum(xRow)
  }}