using lapply with list of arguments on dplyr functions that uses data masking

Question

when programming using dplyr, to programmatically use variables in dplyr vers from function arguments, they need to be references by {{var}}

This works well, but I would like to use lapply with the var argument supplied in a list. This is throwing me an error. I have tried back and forth using substitute and rlang vars like sym but to no avail.

any suggestions? Thanks!

library(tidyverse)
tb <- tibble(a = 1:10, b = 10:1)

foo <- function(var, scalar){
  tb %>% mutate(new_var = {{var}}*scalar)
}

foo(a, pi) #works

lapply(X = list(
  list(sym("a"), pi),
  list(substitute(b), exp(1))), FUN = function(ll) foo(var = ll$a, scalar = ll$pi) ) #err

Allan Cameron · Answer 1 · 2022-11-03T13:39:24.943

You can get round the non-standard evalutation by naming the list elements and using do.call

lapply(X = list(
  list(var = sym("a"), scalar = pi),
  list(var = substitute(b), scalar = exp(1))), 
  FUN = function(ll) do.call(foo, ll))
#> [[1]]
#> # A tibble: 10 x 3
#>        a     b new_var
#>    <int> <int>   <dbl>
#>  1     1    10    3.14
#>  2     2     9    6.28
#>  3     3     8    9.42
#>  4     4     7   12.6 
#>  5     5     6   15.7 
#>  6     6     5   18.8 
#>  7     7     4   22.0 
#>  8     8     3   25.1 
#>  9     9     2   28.3 
#> 10    10     1   31.4 
#> 
#> [[2]]
#> # A tibble: 10 x 3
#>        a     b new_var
#>    <int> <int>   <dbl>
#>  1     1    10   27.2 
#>  2     2     9   24.5 
#>  3     3     8   21.7 
#>  4     4     7   19.0 
#>  5     5     6   16.3 
#>  6     6     5   13.6 
#>  7     7     4   10.9 
#>  8     8     3    8.15
#>  9     9     2    5.44
#> 10    10     1    2.72

^{Created on 2022-11-03 with reprex v2.0.2}

using lapply with list of arguments on dplyr functions that uses data masking

1 Answers1