谢谢大家!tctcab CMCai0104 yufree 问题已经解决!
这里别人教我了另一种比较简单的方法来分享下:
1
v <- seq(1, 50, .5)
embed(v[abs(v-25) <= 1],3)[,3:1]
#> [,1] [,2] [,3]
#> [1,] 24.0 24.5 25.0
#> [2,] 24.5 25.0 25.5
#> [3,] 25.0 25.5 26.0
<sup>Created on 2019-04-04 by the reprex package (v0.2.1)</sup>
2
v <- seq(1, 50, .5)
v1 <- v[which(v == 25) + (-2:2)]
embed(v1, 3)[, 3:1]
#> [,1] [,2] [,3]
#> [1,] 24.0 24.5 25.0
#> [2,] 24.5 25.0 25.5
#> [3,] 25.0 25.5 26.0
<sup>Created on 2019-04-04 by the reprex package (v0.2.1)</sup>
3
library(magrittr)
v <- seq(1, 50, .5)
n <- 3
v[which(v==25) + (-n+1):0 + rep(seq_len(n)-1,each=n)] %>%
matrix(ncol = n)
#> [,1] [,2] [,3]
#> [1,] 24.0 24.5 25.0
#> [2,] 24.5 25.0 25.5
#> [3,] 25.0 25.5 26.0
<sup>Created on 2019-04-04 by the reprex package (v0.2.1)</sup>