Making every other vowel in a vector uppercase

Question

Given a lower case string. Ex:

s <- 'abcdefghijklmnopqrstuvwxyz'

The goal is to make every other vowel in the string an uppercase.

Desired output here:

abcdEfghijklmnOpqrstuvwxyz

As you can see, since all vowels where used in order, e and o where uppercase.

There are only lowercase characters in the strings in all cases.

For aieou, the desired output is:

aIeOu

How could I do this in R?

I tried:

s[unlist(strsplit(s, '')) %in% c('a', 'e', 'i', 'o', 'u')] <- toupper(s[unlist(strsplit(s, '')) %in% c('a', 'e', 'i', 'o', 'u')])

But no avail.

^{Even if this worked, it wouldn't be every other vowel}

R version 4.1.1.

Answer 1

It's not a one-liner, but:

s <- 'abcdefghijklmnopqrstuvwxyz'

as_list <- unlist(strsplit(s, ''))
vowels <- as_list %in% c('a', 'e', 'i', 'o', 'u')
every_other_index <- which(vowels)[c(FALSE, TRUE)]

as_list[every_other_index] <- toupper(as_list[every_other_index])

print(paste(as_list, collapse=''))

gives:

[1] "abcdEfghijklmnOpqrstuvwxyz"

(Use of which taken from this question; use of c(FALSE, TRUE)] from here.)

Answer 2

Another possible solution, using stringr and purrr::map2:

library(tidyverse)

s <- 'abcdefghijklmnopqrstuvwxyz'

s %>% 
  str_split("") %>% unlist %>% 
  map2({1:nchar(s) %in% (str_which(.,"[aeiou]") %>% .[c(F,T)])},
       ~ if_else(.y, str_to_upper(.x),.x)) %>% 
  str_c(collapse = "")

#> [1] "abcdEfghijklmnOpqrstuvwxyz"

Answer 3

Using gregexpr, then gsub, with \\Uppercase pattern replacement.

f <- function(s, u=c('a', 'e', 'i', 'o', 'u')) {
  v <- sort(unlist(sapply(u, \(u) all(unlist(gregexpr(u, s)) > -1))))
  v <- v[seq_along(v) %% 2 == 0]
  gsub(sprintf('(%s)', paste(names(v[v]), collapse='|')), '\\U\\1', s, perl=TRUE)
}

f('abcdefghijklmnopqrstuvwxyz')
# [1] "abcdEfghijklmnOpqrstuvwxyz"

f('world hello')
# [1] "world hEllo"

f('hello world')
# [1] "hEllo world"