Looping varlist using rlang-CodePudding

I'm doing a for inside a function using rlang but it doesn't work.

using r base it works

library(rlang)
library(dplyr)
library(R.utils)

db <- tibble(
  CRT1 = 15*rnorm(10),
  CRT2 = 12*rnorm(10))

f <- function(df, controls) {
  for (i in controls) {
    printf("The control variable is %s \n", i)
  }
}

f(tb2, controls = c("CRT1", "CRT2"))

#The control variable is CRT1 
#The control variable is CRT2

Using rlang

f_rlang = function(data, controls){
  
  controls = enquo(controls)
  
  for (i in controls) {
  printf("The control variable is %s \n", i)
  }
}

f_rlang(db, c(CRT1, CRT2))

#Error in for (i in controls) { : invalid for() loop sequence

CodePudding user response：

I'm not sure if {rlang} itself has a build in functionality to do this, but what you are trying to do mimics the tidy select syntax. So we could use {rlang} together with {tidyselect} to implement this functionality.

This will not only solve your problem, it also adds full tidy select syntax to your function so that we can do f_rlang(db, starts_with("C")):

library(rlang)
library(dplyr)
library(R.utils)

db <- tibble(
  CRT1 = 15*rnorm(10),
  CRT2 = 12*rnorm(10))


f_rlang = function(data, controls){
  
  controls = enexpr(controls)
  
  cols <- tidyselect::eval_select(controls, data)
  
  col_nms <- names(cols)
  
  for (i in col_nms) {
    printf("The control variable is %s \n", i)
  }
}

f_rlang(db, c(CRT1, CRT2))
#> The control variable is CRT1 
#> The control variable is CRT2

f_rlang(db, starts_with("C"))
#> The control variable is CRT1 
#> The control variable is CRT2

^{Created on 2022-09-30 by the reprex package (v2.0.1)}