code: public Datum<SparseArray> remove(int i) {
          Datum<SparseArray> datum = data.remove(i);
  
          n -= datum.x.size();
          for (SparseArray.Entry item : datum.x) {
              colSize[item.i]--;
          }
          
          return datum;
      }
docs: Removes the element at the specified position in this dataset.
  @param i the index of the element to be removed.
  @return the element previously at the specified position.