cur_column() not working in case_when() LHS

[shirdekel]

I want to recode certain columns based on values of columns that have a similar naming. I'm using 1. case_when() to recode, 2. cur_column() to programmatically select the "related" columns, and 3. across() to automatically do this across the relevant columns.

As shown below, I can do this when specifying one column, but not with cur_column(). It complains that it must be used within across(), even though it is being used within across()

library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
library(stringr)

names_list <-
  c("x", "y", "color")

## works

starwars |>
  rename(color = hair_color) |>
  mutate(across(
    skin_color,
    \(x)
    case_when(
      x == "fair" ~ x,
      is.na(!!sym(na.omit(str_extract("skin_color", names_list)))) ~ NA,
      .default = "other"
    )
  )) |>
  select(color, skin_color)
#> # A tibble: 87 × 2
#>    color         skin_color
#>    <chr>         <chr>     
#>  1 blond         fair      
#>  2 <NA>          <NA>      
#>  3 <NA>          <NA>      
#>  4 none          other     
#>  5 brown         other     
#>  6 brown, grey   other     
#>  7 brown         other     
#>  8 <NA>          <NA>      
#>  9 black         other     
#> 10 auburn, white fair      
#> # ℹ 77 more rows

## doesn't work

starwars |>
  rename(color = hair_color) |>
  mutate(across(
    skin_color,
    \(x)
    case_when(
      x == "fair" ~ x,
      is.na(!!sym(na.omit(str_extract(cur_column(), names_list)))) ~ NA,
      .default = "other"
    )
  )) |>
  select(color, skin_color)
#> Error in `cur_column()`:
#> ! Must only be used inside `across()`.

^{Created on 2024-01-15 with reprex v2.1.0}

Session info

sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#>  setting  value
#>  version  R version 4.3.2 (2023-10-31)
#>  os       macOS Sonoma 14.2.1
#>  system   aarch64, darwin23.0.0
#>  ui       unknown
#>  language (EN)
#>  collate  en_AU.UTF-8
#>  ctype    en_AU.UTF-8
#>  tz       Australia/Sydney
#>  date     2024-01-15
#>  pandoc   2.19.2 @ /opt/homebrew/bin/ (via rmarkdown)
#> 
#> ─ Packages ───────────────────────────────────────────────────────────────────
#>  package     * version date (UTC) lib source
#>  cli           3.6.2   2023-12-11 [1] CRAN (R 4.3.2)
#>  digest        0.6.33  2023-07-07 [1] CRAN (R 4.3.2)
#>  dplyr       * 1.1.4   2023-11-17 [1] CRAN (R 4.3.2)
#>  evaluate      0.23    2023-11-01 [1] CRAN (R 4.3.2)
#>  fansi         1.0.6   2023-12-08 [1] CRAN (R 4.3.2)
#>  fastmap       1.1.1   2023-02-24 [1] CRAN (R 4.3.2)
#>  fs            1.6.3   2023-07-20 [1] CRAN (R 4.3.2)
#>  generics      0.1.3   2022-07-05 [1] CRAN (R 4.3.2)
#>  glue          1.7.0   2024-01-09 [1] CRAN (R 4.3.2)
#>  htmltools     0.5.7   2023-11-03 [1] CRAN (R 4.3.2)
#>  knitr         1.45    2023-10-30 [1] CRAN (R 4.3.2)
#>  lifecycle     1.0.4   2023-11-07 [1] CRAN (R 4.3.2)
#>  magrittr      2.0.3   2022-03-30 [1] CRAN (R 4.3.2)
#>  pillar        1.9.0   2023-03-22 [1] CRAN (R 4.3.2)
#>  pkgconfig     2.0.3   2019-09-22 [1] CRAN (R 4.3.2)
#>  purrr         1.0.2   2023-08-10 [1] CRAN (R 4.3.2)
#>  R.cache       0.16.0  2022-07-21 [1] CRAN (R 4.3.2)
#>  R.methodsS3   1.8.2   2022-06-13 [1] CRAN (R 4.3.2)
#>  R.oo          1.25.0  2022-06-12 [1] CRAN (R 4.3.2)
#>  R.utils       2.12.3  2023-11-18 [1] CRAN (R 4.3.2)
#>  R6            2.5.1   2021-08-19 [1] CRAN (R 4.3.2)
#>  reprex        2.1.0   2024-01-11 [1] CRAN (R 4.3.2)
#>  rlang         1.1.2   2023-11-04 [1] CRAN (R 4.3.2)
#>  rmarkdown     2.25    2023-09-18 [1] CRAN (R 4.3.2)
#>  sessioninfo   1.2.2   2021-12-06 [1] CRAN (R 4.3.2)
#>  stringi       1.8.3   2023-12-11 [1] CRAN (R 4.3.2)
#>  stringr     * 1.5.1   2023-11-14 [1] CRAN (R 4.3.2)
#>  styler        1.10.2  2023-08-29 [1] CRAN (R 4.3.2)
#>  tibble        3.2.1   2023-03-20 [1] CRAN (R 4.3.2)
#>  tidyselect    1.2.0   2022-10-10 [1] CRAN (R 4.3.2)
#>  utf8          1.2.4   2023-10-22 [1] CRAN (R 4.3.2)
#>  vctrs         0.6.5   2023-12-01 [1] CRAN (R 4.3.2)
#>  withr         2.5.2   2023-10-30 [1] CRAN (R 4.3.2)
#>  xfun          0.41    2023-11-01 [1] CRAN (R 4.3.2)
#>  yaml          2.3.8   2023-12-11 [1] CRAN (R 4.3.2)
#> 
#>  [1] /opt/homebrew/Cellar/r/4.3.2/lib/R/library
#> 
#> ──────────────────────────────────────────────────────────────────────────────

[nirguk]

I think you can achieve your goal with use of pick() and pull()

(starwars |>
  rename(color = hair_color) |>
  mutate(across(
    skin_color,
    \(x)  case_when(
      x == "fair" ~ x,
      is.na(pull(pick(na.omit(str_extract(cur_column(), names_list))))) ~ NA,
      .default = "other"
    ) )) |>
  select(color, skin_color)

[DavisVaughan]

The !! forces cur_column() to be evaluated immediately, even before the mutate() call. This is a known limitation that we don't have a great solution for right now, but this feels like a somewhat niche case and what @nirguk suggests seems like it would be a bit cleaner anyways