Substring first character from right

Question

I want to be able to substring the first character from the right hand side of each element of a vector

ABC20
BCD3
B1
AB2222
BX4444

so for the group above I would want, C, D, B, B, X .... is there an easy way to this? I know there is a substr and a numindex/charindex. So I think I can use these but not sure exactly in R.

related: [regex](https://stackoverflow.com/questions/4736/learning-regular-expressions) — jogo, Feb 21 '18 at 08:07

Sotos · Accepted Answer · 2018-02-21T08:25:42.737

3

You can use library stringi,

stringi::stri_extract_last_regex(x, '[A-Z]')
#[1] "C" "D" "B" "B" "X"

DATA

x <- c('ABC20', 'BCD3', 'B1', 'AB2222', 'BX4444')

edited Feb 21 '18 at 08:25

answered Feb 21 '18 at 08:07

Sotos

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akrun · Answer 2 · 2018-02-21T09:25:34.407

0

We can use sub to capture the last upper case letter (([A-Z])) followed by zero or more digits (\\d*) until the end ($) of the string and replace it with the backreference (\\1) of the captured group

sub(".*([A-Z])\\d*$", "\\1", x)
#[1] "C" "D" "B" "B" "X"

data

x <- c("ABC20", "BCD3", "B1", "AB2222", "BX4444")

edited Feb 21 '18 at 09:25

answered Feb 21 '18 at 08:04

akrun

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When I added my answer with `stringi`, it was NOT in your answer. – Sotos Feb 21 '18 at 08:15
@Sotos I was adding the same answer and I didn't find a new answer – akrun Feb 21 '18 at 08:15
Ok. I m just saying. I posted it and yours only had the `sub` solution. – Sotos Feb 21 '18 at 08:17
@Sotos I was updating at that time. Once I posted, I find yours too – akrun Feb 21 '18 at 08:17
1

@Sotos I removed the answer. What I meant is that I came up with the answer independently. By checking the timings, you posted it first. It is a fair argument. Having said that, I noticed many times others posting the same answer as mine (that too after 5 or 10 mins) and if I comment, then the obvious reaction would be `when i started typing there was no answer`. – akrun Feb 21 '18 at 10:44
1

I agree. Thank you for that. – Sotos Feb 21 '18 at 12:25

score 0 · Answer 3 · answered Feb 21 '18 at 08:15

Try this:

Your data:

  list<-c("ABC20","BCD3","B1","AB2222","BX4444")

Identify position

  number_pos<-gregexpr(pattern ="[0-9]",list)
  number_first<-unlist(lapply(number_pos, `[[`, 1))

Extraction

  substr(list,number_first-1,number_first-1)
[1] "C" "D" "B" "B" "X"

Substring first character from right

3 Answers3

data