用于从另外两个矩阵索引中重构矩阵的循环

I've got two matrix with same numbers of rows and columns, and I would like to merge them by their index in order to create a new matrix (I don't know nrow() nor ncol() in advance, nrow() comes from k kmeans clusters centroid and ncol() comes from k' knn values)I've got two matrix with same numbers of rows a