separate_cols()

tidyr::separate() cannot handle the cell that contains arbitrary order of values. separate_rows() + pivot_wider() works to some extent, but this cannot handle an empty string or a missing value.

tibble(
  id = 1:4,
  answer = c("a,b", "a,c", "a,b,c", "c")
) %>% 
  # separate() だとできないのでいったん縦向きに広げてから pivot する
  separate_rows(answer) %>% 
  # pivot するのに適当な値が必要
  dplyr::mutate(t = TRUE) %>% 
  pivot_wider(names_from = answer, values_from = t, values_fill = FALSE)
#> # A tibble: 4 x 4
#>      id a     b     c    
#>   <int> <lgl> <lgl> <lgl>
#> 1     1 TRUE  TRUE  FALSE
#> 2     2 TRUE  FALSE TRUE 
#> 3     3 TRUE  TRUE  TRUE 
#> 4     4 FALSE FALSE TRUE

This function is for the case.

library(dplyr, warn.conflicts = FALSE)

separate_cols <- function(x, sep = ",") {
  # str_split() returns a list of split character vectors
  s <- stringr::str_split(x, sep)

  all_cols <- unique(purrr::flatten_chr(s))
  all_cols <- all_cols[!is.na(all_cols) & all_cols != ""]
  tmpl <- tibble::tibble(.rows = 1L)
  tmpl[1L, all_cols] <- FALSE
  
  s <- s %>% 
    purrr::map(
      ~ {
        if (identical(.x, "") || is.na(.x)) {
          tmpl
        } else {
          tmpl[1L, .x] <- TRUE
          tmpl
        }
      }
    )
  
  dplyr::bind_rows(s)
}

separate_cols(c("a,b", "a,c", "a,b,c", "", NA))
#> # A tibble: 5 x 3
#>   a     b     c    
#>   <lgl> <lgl> <lgl>
#> 1 TRUE  TRUE  FALSE
#> 2 TRUE  FALSE TRUE 
#> 3 TRUE  TRUE  TRUE 
#> 4 FALSE FALSE FALSE
#> 5 FALSE FALSE FALSE

tibble(
  id = 1:5,
  answer = c("a,b", "a,c", "a,b,c", "", NA)
) %>%
  mutate(separate_cols(answer), .keep = "unused")
#> # A tibble: 5 x 4
#>      id a     b     c    
#>   <int> <lgl> <lgl> <lgl>
#> 1     1 TRUE  TRUE  FALSE
#> 2     2 TRUE  FALSE TRUE 
#> 3     3 TRUE  TRUE  TRUE 
#> 4     4 FALSE FALSE FALSE
#> 5     5 FALSE FALSE FALSE

yutannihilation/separate_cols.md