如何避免 R 中的循环:从列表中选择项目 [英] How to avoid a loop in R: selecting items from a list

问题描述

我可以使用循环来解决这个问题，但我尝试在向量中思考，因此我的代码将更具 R 风格.

I could solve this using loops, but I am trying think in vectors so my code will be more R-esque.

我有一个名字列表.格式为名字_姓氏.我想从这个列表中删除一个只有名字的单独列表.我似乎无法理解如何做到这一点.以下是一些示例数据:

I have a list of names. The format is firstname_lastname. I want to get out of this list a separate list with only the first names. I can't seem to get my mind around how to do this. Here's some example data:

t <- c("bob_smith","mary_jane","jose_chung","michael_marx","charlie_ivan")
tsplit <- strsplit(t,"_")

看起来像这样:

> tsplit
[[1]]
[1] "bob"   "smith"

[[2]]
[1] "mary" "jane"

[[3]]
[1] "jose"  "chung"

[[4]]
[1] "michael" "marx"   

[[5]]
[1] "charlie" "ivan"   

我可以使用这样的循环得到我想要的:

I could get out what I want using loops like this:

for (i in 1:length(tsplit)){
    if (i==1) {t_out <- tsplit[[i]][1]} else{t_out <- append(t_out, tsplit[[i]][1])} 
}

这会给我这个:

t_out
[1] "bob"     "mary"    "jose"    "michael" "charlie"

那么我如何在没有循环的情况下做到这一点?

So how can I do this without loops?

推荐答案

您可以使用apply(或sapply)

t <- c("bob_smith","mary_jane","jose_chung","michael_marx","charlie_ivan")
f <- function(s) strsplit(s, "_")[[1]][1]
sapply(t, f)

bob_smith    mary_jane   jose_chung michael_marx charlie_ivan 

       "bob"       "mary"       "jose"    "michael"    "charlie" 

参见:简要介绍在 R 中应用"

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