使用所有向量元素的组合粘贴两个向量 [英] Pasting two vectors with combinations of all vectors' elements

问题描述

我有两个向量:

vars <- c("SR", "PL")
vis <- c(1,2,3)

基于这些向量，我想创建以下向量:

Based on these vectors I would like to create the following vector:

"SR.1"  "SR.2"  "SR.3"  "PL.1"  "PL.2"  "PL.3"

对于paste，我得到以下结果:

With paste I have the following result:

paste(vars, vis, sep=".")
 [1] "SR.1" "PL.2" "SR.3"

如何创建所需的载体?

推荐答案

您可以使用它，但是可能有一个更简单的解决方案:

You can use this, but there may be a simpler solution :

R> apply(expand.grid(vars, vis), 1, paste, collapse=".")
[1] "SR.1" "PL.1" "SR.2" "PL.2" "SR.3" "PL.3"

---

expand.grid返回一个data.frame，当与apply一起使用时，apply会将其转换为matrix.这只是不必要的(并且在大数据上效率低下). outer给出matrix并接受函数参数.在海量数据上也将非常有效.

---

expand.grid gives back a data.frame which when used with apply, apply will convert it to a matrix. This is just unnecessary (and inefficient on large data). outer gives a matrix and also takes function argument. It'll be much efficient on huge data as well.

使用outer:

as.vector(outer(vars, vis, paste, sep="."))
# [1] "SR.1" "PL.1" "SR.2" "PL.2" "SR.3" "PL.3"

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