CODEWITHSUNDEEP
rstringdata-manipulation
Moose
Moose

Reputation: 275

Extract letters from a string in R

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").

Because the number of letters varies, I cannot use substring to specify the first and last characters.

How can I go about this?

Upvotes: 17

Views: 48615

Answers (5)

Bernard Beckerman
Bernard Beckerman

Reputation: 165

The previous answers seem more complicated than necessary. This question regarding digits also works with letters:

> 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"

Upvotes: 16

centaur
centaur

Reputation: 21

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.

The simplest and fastest solution I found myself: 

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:

[1] "AB"  "GF"  "ABC"

Hope this helps someone!

Upvotes: 2

cephalopod
cephalopod

Reputation: 1906

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: 

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 = " ")

Upvotes: 3

mimoralea
mimoralea

Reputation: 9976

None of the answers work if you have mixed letter with spaces. Here is what I'm doing for those cases:

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"

Upvotes: 2

Mamoun Benghezal
Mamoun Benghezal

Reputation: 5314

you can try 

sub("^([[:alpha:]]*).*", "\\1", x)
[1] "AB"  "GF"  "ABC"

Upvotes: 11

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