Using `case_when()` instead of `if_else`

I'm trying to use case_when() instead of if_else when I ran into some problems:

# if_else version:  (x<- c("apple", "orange", "grapes", "kiwi"))  longstr <- function(x, delim = ",") {    n <- length(x)    if (n == 0) {      ""    } else if (n == 1) {      x    } else if (n == 2) {      str_c(x[[1]], "&", x[[2]], sep = " ")    } else {      front <- str_c(x[seq_len(n - 1)], delim)      back <- str_c("&", x[[n]], sep = " ")      str_c(c(front, back), collapse = " ")    }  }    longstr(x) # gives "apple, orange, grapes, & kiwi"  longstr(c("pea", "pod") # gives "pea & pod"  longstr("egg") # gives "egg"    

but somehow when I rewrite this using case_when, things start to be weird:

# case_when version:  longstr2 <- function(x, delim = ",") {    n <- length(x)    case_when(      n == 0 ~ "",      n == 1 ~ x,      n == 2 ~ str_c(x[1], "&", x[2], sep = " "),   # weird 1: I can't use x[[1]], but must use only x[1] here      TRUE ~ {        not_last <- str_c(x[seq_len(n - 1)], delim)        last <- str_c("&", x[[n]], sep = " ")       # but somehow here I can still use x[[n]]        (str_c(c(not_last, last), collapse = " "))}    )  }    # the weirdest thing:  longstr2(x)       # gives "apple, orange, grapes, & kiwi" "apple, orange, grapes, & kiwi" "apple, orange, grapes, & kiwi" "apple, orange, grapes, & kiwi"      # I don't know why it repeats 4 times  longstr2(c("pea", "pod")       # gives "pea & pod" "pea & pod"      # here it repeats 2 times  longstr2("egg") # gives "egg"    

I know somehow the weird repeat is linked to my n, but I don't know exactly where it went wrong. Any pointer appreciated! thank you!

https://stackoverflow.com/questions/67259659/using-case-when-instead-of-if-else April 26, 2021 at 09:04AM