string 从 R 中的字符串中提取字母
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Extract letters from a string in R
提问by Moose
I have a character vector containing variable names such as x <- c("AB.38.2", "GF.40.4", "ABC.34.2"). I want to extract the letters so that I have a character vector now containing only the letters e.g. c("AB", "GF", "ABC").
我有一个包含变量名称的字符向量，例如x <- c("AB.38.2", "GF.40.4", "ABC.34.2"). 我想提取字母，以便我有一个字符向量，现在只包含字母，例如c("AB", "GF", "ABC").
Because the number of letters varies, I cannot use substringto specify the first and last characters.
因为字母的数量不同，所以我不能substring用来指定第一个和最后一个字符。
How can I go about this?
我该怎么办？
采纳答案by Mamoun Benghezal
you can try
你可以试试
sub("^([[:alpha:]]*).*", "\1", x)
[1] "AB" "GF" "ABC"
回答by Bernard Beckerman
The previous answers seem more complicated than necessary. This questionregarding digits also works with letters:
以前的答案似乎比必要的要复杂。这个关于数字的问题也适用于字母：
> x <- c("AB.38.2", "GF.40.4", "ABC.34.2", "A B ..C 312, Fd", " a")
> gsub("[^a-zA-Z]", "", x)
[1] "AB" "GF" "ABC" "ABCFd" "a"
回答by mimoralea
None of the answers work if you have mixed letter with spaces. Here is what I'm doing for those cases:
如果您将字母与空格混合在一起，则所有答案都不起作用。这是我为这些情况所做的：
x <- c("AB.38.2", "GF.40.4", "ABC.34.2", "A B ..C 312, Fd")
unique(na.omit(unlist(strsplit(unlist(x), "[^a-zA-Z]+"))))
[1] "AB" "GF" "ABC" "A" "B" "C" "Fd"
[1]“AB”“GF”“ABC”“A”“B”“C”“Fd”
回答by cephalopod
This is how I managed to solve this problem. I use this because it returns the 5 items cleanly and I can control if i want a space in between the words:
这就是我设法解决这个问题的方法。我使用它是因为它干净地返回了 5 个项目，我可以控制是否要在单词之间留一个空格：
x <- c("AB.38.2", "GF.40.4", "ABC.34.2", "A B ..C 312, Fd", " a")
extract.alpha <- function(x, space = ""){
require(stringr)
require(purrr)
require(magrittr)
y <- strsplit(unlist(x), "[^a-zA-Z]+")
z <- y %>% map(~paste(., collapse = space)) %>% simplify()
return(z)}
extract.alpha(x, space = " ")回答by Lenz Paul
I realize this is an old question but since I was looking for a similar answer just now and found it, I thought I'd share.
我意识到这是一个老问题，但由于我刚刚正在寻找类似的答案并找到了它，我想我会分享。
The simplest and fastest solution I found myself:
我发现自己最简单，最快的解决方案：
x <- c("AB.38.2", "GF.40.4", "ABC.34.2")
only_letters <- function(x) { gsub("^([[:alpha:]]*).*$","\1",x) }
only_letters(x)
And the output is:
输出是：
[1] "AB" "GF" "ABC"
Hope this helps someone!
希望这可以帮助某人！
