r语言 - 一种更快(矢量化)的方法，用于创建具有预定长度的 1 和 0 的滑动序列

Question

>我有以下函数可以工作，但我觉得有一种更快的（矢量化或包或内置？）方法来编写这个？

create_seq <- function(n, len) {
  mat <- matrix(nrow = length(0:(n-len)), ncol = n)
  for(i in 0:(n-len)) {
    mat[i + 1, ] <- c(rep(0L, i), rep(1L, len), rep(0L, n - (len + i)))
  }
  return(mat)
}
create_seq(10, 3)
#>      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
#> [1,]    1    1    1    0    0    0    0    0    0     0
#> [2,]    0    1    1    1    0    0    0    0    0     0
#> [3,]    0    0    1    1    1    0    0    0    0     0
#> [4,]    0    0    0    1    1    1    0    0    0     0
#> [5,]    0    0    0    0    1    1    1    0    0     0
#> [6,]    0    0    0    0    0    1    1    1    0     0
#> [7,]    0    0    0    0    0    0    1    1    1     0
#> [8,]    0    0    0    0    0    0    0    1    1     1
create_seq(10, 5)
#>      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
#> [1,]    1    1    1    1    1    0    0    0    0     0
#> [2,]    0    1    1    1    1    1    0    0    0     0
#> [3,]    0    0    1    1    1    1    1    0    0     0
#> [4,]    0    0    0    1    1    1    1    1    0     0
#> [5,]    0    0    0    0    1    1    1    1    1     0
#> [6,]    0    0    0    0    0    1    1    1    1     1
create_seq(7, 2)
#>      [,1] [,2] [,3] [,4] [,5] [,6] [,7]
#> [1,]    1    1    0    0    0    0    0
#> [2,]    0    1    1    0    0    0    0
#> [3,]    0    0    1    1    0    0    0
#> [4,]    0    0    0    1    1    0    0
#> [5,]    0    0    0    0    1    1    0
#> [6,]    0    0    0    0    0    1    1

Answer 1

创建一个稀疏带状矩阵：

library(Matrix)    
create_seq_sparse <- function(n, len) {
  bandSparse(m = n, n = n - len + 1L, k = seq_len(len) - 1L)
}
create_seq_sparse(10, 3)
# 8 x 10 sparse Matrix of class "ngCMatrix"
# 
# [1,] | | | . . . . . . .
# [2,] . | | | . . . . . .
# [3,] . . | | | . . . . .
# [4,] . . . | | | . . . .
# [5,] . . . . | | | . . .
# [6,] . . . . . | | | . .
# [7,] . . . . . . | | | .
# [8,] . . . . . . . | | |
create_seq_sparse(7, 2)
#6 x 7 sparse Matrix of class "ngCMatrix"
#
#[1,] | | . . . . .
#[2,] . | | . . . .
#[3,] . . | | . . .
#[4,] . . . | | . .
#[5,] . . . . | | .
#[6,] . . . . . | |

如果需要密集的数值矩阵，可以使用+as.matrix(...)作为最后一步。

Answer 2

函数

的矢量化基本R变体：

create_seq <- function(n, len){
  x <- c(rep(1, len), rep(0, (n - len + 1)))
  y <- rep(x, ceiling(((n - len + 1) * n)/length(x)))
  matrix(y[1:((n - len + 1) * n)], nrow = n - len + 1, ncol = n, byrow = T)
}

这可以缩短为：

create_seq <- function(n, len){
  matrix(rep(c(rep(1, len), rep(0, (n-len+1)))
             , ceiling(((n-len+1)*n)/(n + 1)))[1:((n-len+1)*n)], 
         nrow = n - len + 1, ncol = n, byrow = T)
}
> create_seq(7, 4)
     [,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,]    1    1    1    1    0    0    0
[2,]    0    1    1    1    1    0    0
[3,]    0    0    1    1    1    1    0
[4,]    0    0    0    1    1    1    1
> create_seq(5, 2)
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    1    0    0    0
[2,]    0    1    1    0    0
[3,]    0    0    1    1    0
[4,]    0    0    0    1    1