复制向量的每个元素，并将“ a”添加到奇数，将“ b”添加到偶数

Question

这是我的原始向量（长度可能会有所不同）

c("e1","e2","e3","e4","e5","e6","e7","e8","e9","e10")

我想复制每个元素（保持顺序）并将属性“ a”赋给第一个匹配项，将“ b”赋给第二个出现，以得到：

c("e1a","e1b","e2a","e2b","e3a","e3b","e4a","e4b","e5a","e5b","e6a","e6b","e7","e7b","e8a","e8b","e9a","e9b","e10a","e10b")

如何在R中以一种简洁的方式做到这一点？

Answer 1

您可以使用rep(each = 2)来获取重复项，然后使用paste0来添加后缀字母，如下所示。

这是向量回收的一个很好的例子； paste0将使用c("a", "b")的元素，直到较长向量的长度自动耗尽为止。因此，您可以使用原始vec的任何长度来执行此操作。许多base和package R函数将执行类似的操作。

vec <- c("e1","e2","e3","e4","e5","e6","e7","e8","e9","e10")
paste0(rep(vec, each = 2), c("a", "b"))
#>  [1] "e1a"  "e1b"  "e2a"  "e2b"  "e3a"  "e3b"  "e4a"  "e4b"  "e5a"  "e5b" 
#> [11] "e6a"  "e6b"  "e7a"  "e7b"  "e8a"  "e8b"  "e9a"  "e9b"  "e10a" "e10b"

由reprex package（v0.2.0）于2018-08-07创建。