[jira] [Created] (ARROW-13118) [R] Improve handling of R scalars in some nse_funcs

["Ian Cook (Jira)" <ji...@apache.org>]

Ian Cook created ARROW-13118:
--------------------------------

             Summary: [R] Improve handling of R scalars in some nse_funcs
                 Key: ARROW-13118
                 URL: https://issues.apache.org/jira/browse/ARROW-13118
             Project: Apache Arrow
          Issue Type: Improvement
          Components: R
            Reporter: Ian Cook
            Assignee: Ian Cook
             Fix For: 5.0.0


Some of the functions in {{nse_funcs}} do not behave properly when passed R scalar input in expressions in dplyr verbs. Some examples:
{code:r}
Table$create(x = 1) %>% mutate(as.character(42))
Table$create(x = 1) %>% mutate(is.character(("foo")))
Table$create(x = 1) %>% mutate(nchar("foo"))
Table$create(x = 1) %>% mutate(is.infinite(Inf))
{code}
This could be resolved by using {{build_expr()}} instead of {{Expression$create()}}, but {{build_expr()}} is awfully heavy. The only part of it we really need to make this work is this:
{code:r}
    args <- lapply(args, function(x) {
      if (!inherits(x, "Expression")) {
        x <- Expression$scalar(x)
      }
      x
    }){code}
Maybe we could make a function called {{wrap_r_scalar}}, like this:
{code:r}
wrap_r_scalar <- function(x) {
  if (!inherits(x "Expression")) {
    assert_that(
      length(x) == 1,
      msg = "Literal vectors of length != 1 not supported"
    )
    Expression$scalar(x)
  } else {
    x
  }
}
{code}
and use it as needed in various of the {{nse_funcs}} functions.



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