Variable scoping issue with .data inside lambda Ffunction used in across()

[bakaburg1]

Hello,

This error was driving me crazy and took me a while to isolate it. if one wants to use .data into a lambda function into across, you cannott index .data with variables created into the lambda function itself, otherwise R will complain that such variable doesn't exist!

example:

iris |> mutate(
    across("Sepal.Length", \(x) {
        other_col_name <- "Sepal.Width"

        other_col_val <- .data[[other_col_name]]

        x + other_col_val
    })
)
> Error in .f(.x[[i]], ...) : object 'other_col_name' not found

Which was driving me crazy, since the variable clearly exists in the scope.

but if other_col_name is defined outside no problem:

other_col_name <- "Sepal.Width"
iris |> mutate(
    across("Sepal.Length", \(x) {

        other_col_val <- .data[[other_col_name]]

        x + other_col_val
    })
)
# All fine

If this is by design and you don't plan to fix it, could be useful to have a clearer error and some extra documentation somewhere!

There cases in which for example the index name is defined dynamically based on the x or cur_column() value. Now that I now the issue I'll use pick()[1], unless you have better solutions.

[MrFlick]

I noticed a possibly related problem from this Stack Overflow question. This code results in an error

iris |>
  group_nest(Species) |>
  mutate(boo = map(data, function(x) {
    colsym <- sym("Sepal.Length")
    x %>% mutate(newcol =! !colsym)
  }))
# Error: object 'colsym' not found

Same issue if using .data

iris |>
  group_nest(Species) |>
  mutate(boo = map(data, function(x) {
    colname <- "Sepal.Length"
    x %>% mutate(uncle=.data[[colname]])
  }))

But if you define the function first rather than inline, it will run

helper <- \(x) {
  colsym <- sym("Sepal.Length")
  x %>% mutate(newcol=!!colsym)
}

iris |>
  group_nest(Species) |>
  mutate(data = map(data, helper))

Looking at the trace, it seems the problem is actually coming from rlang::quos. Something else that will trigger the error is

quos(\(x) {bee <- colsym::sym("a"); mutate(x, newcol=!!colsym)})

Basically the !! part is being evaluated when defining the function, not when calling the function. Is there a way to delay the evaluation of the !! or .data[[]] when applied to functions? Tested with rlang_1.1.3, purrr_1.0.2, dplyr_1.1.4

[moodymudskipper]

You'd have the same issue if you nest bquote() calls, the .() are substituted by the outside calls, similar if you nest substitute() calls.

You can use the following trick:

protect <- function(expr) call("!", call("!", substitute(expr)))
rlang::expr(!!protect(hello))
#> !!hello
library(tidyverse)
#> Warning: package 'ggplot2' was built under R version 4.2.3
#> Warning: package 'stringr' was built under R version 4.2.3
iris |>
  group_nest(Species) |>
  mutate(boo = map(data, function(x) {
    colsym <- sym("Sepal.Length")
    x %>% mutate(newcol = !!protect(colsym))
  }))
#> # A tibble: 3 × 3
#>   Species                  data boo              
#>   <fct>      <list<tibble[,4]>> <list>           
#> 1 setosa               [50 × 4] <tibble [50 × 5]>
#> 2 versicolor           [50 × 4] <tibble [50 × 5]>
#> 3 virginica            [50 × 4] <tibble [50 × 5]>

For data it's a bit different I think, in the given examples .data shouldn't be used, it's not to be considered as an object in scope, but as a special operator at the top level for mutate, it's not very clear from the dot though. It seems a macro is run (so if you set a browser() in the function it won't be triggered for instance) when we use .data, where using means calling it with brackets. This works around it :

iris |>
  group_nest(Species) |>
  mutate(boo = map(data, ~ {
    colname <- "Sepal.Length"
    .x %>% mutate(uncle= (.data)[[colname]])
  }))
#> # A tibble: 3 × 3
#>   Species                  data boo              
#>   <fct>      <list<tibble[,4]>> <list>           
#> 1 setosa               [50 × 4] <tibble [50 × 5]>
#> 2 versicolor           [50 × 4] <tibble [50 × 5]>
#> 3 virginica            [50 × 4] <tibble [50 × 5]>