Split Character String Using Only Last Delimiter in r

Question

I have a character variable that I would like to split into 2 variables based on a \"-\" delimiter, however, I would only like to split based on the last delimiter as there

Answer 1

You can try using gregexpr :

a=c("foo - bar","hey-now-man","say-now-girl","fine-now")
lastdelim = tail(gregexpr("-",a)[[1]],n=1)
output1 = sapply(a,function(x) {substr(x,1,lastdelim-1)})
output2 = sapply(a,function(x) {substr(x,lastdelim+1,nchar(x))})

Answer 2

A solution based on stringi and data.table: reverse the string and split it into fixed items and then reverse back:

library(stringi)
x <- c('foo - bar', 'hey-now-man', 'say-now-girl', 'fine-now')

lapply(stri_split_regex(stri_reverse(x), pattern = '[-\\s]+', n = 2), stri_reverse)

If we want to make a data.frame with this:

y <- lapply(stri_split_regex(stri_reverse(x), pattern = '[-\\s]+', n = 2), stri_reverse)

y <- setNames(data.table::transpose(y)[2:1], c('output1', 'output2'))

df <- as.data.frame(c(list(input = x), y))

# > df
# input output1 output2
# 1    foo - bar     foo     bar
# 2  hey-now-man hey-now     man
# 3 say-now-girl say-now    girl
# 4     fine-now    fine     now

Answer 3

Using unglue you would do :

# install.packages("unglue")
library(unglue)
df <- data.frame(input = c("foo - bar","hey-now-man","say-now-girl","fine-now"))
unglue_unnest(df, input, "{output1}{=\\s*-\\s*}{output2=[^-]+}", remove = FALSE)
#>          input output1 output2
#> 1    foo - bar     foo     bar
#> 2  hey-now-man hey-now     man
#> 3 say-now-girl say-now    girl
#> 4     fine-now    fine     now

^{Created on 2019-11-06 by the reprex package (v0.3.0)}

Answer 4

You can also use a negative lookahead:

df <- tibble(input = c("foo - bar", "hey-now-man", "say-now-girl", "fine-now"))

df %>% 
    separate(input, into = c("output1", "output2"), sep = "\\-(?!.*-)", remove = FALSE)

Refs:

[1] https://frightanic.com/software-development/regex-match-last-occurrence/

[2] https://www.regular-expressions.info/lookaround.html