Using the %in% operator to compare values across columns

[iyedg]

Firstly thank you so much for creating this package, I am very thankful.

I have a situation where I want to check that values in a column a must be one of the values in columns b and c. Based on the data frame in the following reprex, I would expect rows 2, 4, and 5 to be in violation of such rule defined with the %in% operator, but that is not the case.

library(validate)

example_df <- tibble::tribble(
  ~a, ~b, ~c,
  "a", "a", "b", # a exists in b, c
  "a", "x", "z", # a does not exist in b, c
  "a", "a", NA_character_, # a exists in b, c but one of them is NA
  "a", "x", NA_character_, # a does not exist in b, c but one of them is NA,
  NA_character_, "a", "x", # a is NA but not NA in b and c
  NA_character_, NA_character_, "x" # a is na and b or c is na
)

result <- example_df |> check_that(
  a %in% c(b, c) 
)

violating(example_df, result)
#> # A tibble: 0 × 3
#> # ℹ 3 variables: a <chr>, b <chr>, c <chr>

^{Created on 2023-11-04 with reprex v2.0.2}

I am aware that I can simulate the %in% operator with

result <- example_df |> check_that(
  a == b | a == c
)

But this would get too hard to maintain as the number of columns grows.

What is the recommended way to write such a check ?

Thanks