Vector.Element element = sparseRowIterator.next(); int col = element.index(); setQuick(row, col, function.apply(element.get(), other.getQuick(row, col))); setQuick(row, col, function.apply(getQuick(row, col), other.getQuick(row, col))); "implementation."); for (int col = 0; col < columns; col++) { setQuick(row, col, function.apply(getQuick(row, col), other.getQuick(row, col)));