Regex's are working, but code looks horrible - r

Question

I'm cleaning up a long list of noun-phrases for further text mining. They're supposed to be 1- or 2-word phrases, but some have / in a conjunction. Here's what I've got:
library(tidyverse)
conjuncts <- tibble(usecase = 1:3,
classes = c("Insulators/Insulation",
"Optic/light fiber",
"Magnets"))
And I want:
wanted <- tibble(usecase = c(1,1,2,2,3),
classes = c("Insulators/Insulation",
"Insulators/Insulation",
"Optic/light fiber",
"Optic/light fiber",
"Magnets"),
bigrams = c("Insulators", "Insulation",
"Optic fiber", "Light fiber", NA))
I've got something working, but it's horrible and non-extensible.
patternSplit <- function(class){
regexs <- c("(?x) ^ (\\w+) / (\\w+) $",
"(?x) ^ (\\w+) / (\\w+) \\s+ (\\w+) $")
if(str_detect(class, regexs[1])){
extr <- str_match(class, regexs[1])
list(extr[1,2],
extr[1,3])
} else if(str_detect(class, regexs[2])){
extr <- str_match(class, regexs[2])
list(paste(extr[1,2], extr[1,4]),
paste(extr[1,3], extr[1,4]))
} else {
list(NA_character_)
}
}
anx <- conjuncts %>%
mutate(bigrams = map(classes, patternSplit)) %>%
unnest(cols = "bigrams") %>%
unnest(cols = "bigrams")
Which gives me what I wanted, but blecchh!
# A tibble: 5 x 3
usecase classes bigrams
<int> <chr> <chr>
1 1 Insulators/Insulation Insulators
2 1 Insulators/Insulation Insulation
3 2 Optic/light fiber Optic fiber
4 2 Optic/light fiber light fiber
5 3 Magnets NA
The top two problems (1) I have to run the rexex twice - once with str_detect to get the logical for the if / else and again with str_match to pull out the tokens. (2) I have do the double unnest to unwind the list structure. And smaller problem (3) Can I get out of if / else, into case_when or switch?
I'll eventually be extending this to about a dozen patterns and use-cases.

Answer 1

Here is solution using / as seperator to detect word phrases, then using ifelse to get desired result:
patternSplit<- function(x,p="[A-z]+[/][A-z]+"){
x1<- stringr::str_extract(x,p)
x2<- stringr::str_replace(x,p,"")
return(cbind(val1=x1,val2=x2))
}
conjuncts<- cbind(conjuncts,conjuncts$classes %>% patternSplit()) %>%
tidyr::separate_rows(val1, sep = '/') %>%
dplyr::mutate(bigrams= ifelse(!is.na(val1),paste0(val1,val2),val1)) %>%
dplyr::select(-contains("val"))
conjuncts
usecase classes bigrams
1 1 Insulators/Insulation Insulators
2 1 Insulators/Insulation Insulation
3 2 Optic/light fiber Optic fiber
4 2 Optic/light fiber light fiber
5 3 Magnets <NA>