Error with tidy select when feeding column names into purrr::map for user function-CodePudding

I have a long function that uses a dataframe column name as an input and am trying to apply it to several different column names without a new line of code each time. I am having issues with tidyselect within the function called by map. I believe the issue is related to defusing, but I cannot figure it out. A toy example using mtcars data is below.

This works correctly with map:

  library(tidyverse)

  sum_dplyr <- function(df, x) {
    
    res <- df %>% summarise(mean = mean({{x}}, na.rm = TRUE))
    
    return(res)
    
  } 
  
  sum_dplyr(mtcars, disp)
  
  map(names(mtcars), ~ sum_dplyr(mtcars, mtcars[[.]])) # all columns -> works fine

While this gives the error "Must subset columns with a valid subscript vector" when feeding the function through map:

  library(tidyverse)

  sel_dplyr <- function(df, x) {
    
    res <- df %>% dplyr::select({{x}})
    
    return(res)
    
  } 
  
  sel_dplyr(mtcars, disp) # ok
  
  map(names(mtcars), ~ sel_dplyr(mtcars, mtcars[[.]])) # all columns -> error

What am I missing here ? Many thanks !

CodePudding user response：

It may be better to correct the function to make sure that it takes both unquoted and quoted. With map, we are passing a character string. So, instead of {{}}, can use ensym with !!

sum_dplyr <- function(df, x) {
    x <- rlang::ensym(x)
    res <- df %>% 
         summarise(mean = mean(!!x, na.rm = TRUE))
    
    return(res)
    
  }

Similarly for sel_dplyr

sel_dplyr <- function(df, x) {
    x <- rlang::ensym(x)
    res <- df %>% 
         dplyr::select(!! x)
    
    return(res)
    
}

and then test as

library(purrr)
library(dplyr)
map(names(mtcars), ~ sel_dplyr(mtcars, !!.x)) 
sel_dplyr(mtcars, carb)