Use a specific column inside the user defined function for summarize function in dplyr

Question

I have the following question. I have a dataset mtcars and I want to write a a function to summarize the given variable, e.g. mpg given that another variable has a particular value, e.g. vs = 1. I provide a code, where I want to summarize mpg given that vs = 1 and again summarize given that am = 1.

Error in NextMethod("[") : object 'vs' not found

f_1 <- function(data, var){
  
  # Quote the variable that we can use it's name
  var         <- enquo(var)
  
  data %>%
    summarize(p_1          = mean(!!var[vs  == 1], na.rm = TRUE),
              p_2          = mean(!!var[am  == 1], na.rm = TRUE))
}


f_1(data = mtcars, var = mpg)

Answer 1

You can use curly-curly ({{..}}) :

library(dplyr)

f_1 <- function(data, var){
  data %>%
    summarize(p_1 = mean({{var}}[vs  == 1], na.rm = TRUE),
              p_2 = mean({{var}}[am  == 1], na.rm = TRUE))
}

f_1(data = mtcars, var = mpg)

#      p_1      p_2
#1 24.55714 24.39231