有没有办法重新排序矩阵的行和列以创建一个密集的角，在R？

I have a large matrix which comprises 1,2 and missing (coded as NA) values. The matrix has 500000 rows by 10000 columns. There are approximately 0.05% 1- or 2-values, and the remaining values are NA.I have a large matrix which comprises 1,2 and m