Question

我有一个n * n矩阵，想选择行号大于其列号的这些数据。

我尝试在R中使用循环，但问题是速度太慢。

matrix_new <- NULL

for (i in 1:nrow(matrix)) {
  for (j in 1:ncol(matrix)) {
    if (i > j) {
      matrix_new <- c(matrix_new, matrix[i,j]) 
    }
  }
}

R中的双循环似乎很慢。是否有任何有效的方法可以做到这一点？

Answer 1

下三角矩阵有一个基本的R函数：

m[lower.tri(m, diag = F)]

Answer 2

$ awk 'NR==4{$0=(sub(/^#/,"") ? "" : "#") $0} 1' file
what are you doing now?
what are you gonna do? stab me?
this is interesting.
#This is a test.
go big
don't be rude.

$ awk 'NR==4{$0=(sub(/^#/,"") ? "" : "#") $0} 1' file |
  awk 'NR==4{$0=(sub(/^#/,"") ? "" : "#") $0} 1'
what are you doing now?
what are you gonna do? stab me?
this is interesting.
This is a test.
go big
don't be rude.

Answer 3

我们可以使用row/col

创建一个逻辑条件

mat[row(mat) > col(mat)]

有效过滤行数大于列数的n * n矩阵

3 个答案: