CODEWITHSUNDEEP
rfunctionrlang
runningbirds
runningbirds

Reputation: 6615

passing in expression as an argument in r

I'm struggling to understand the issues with passing in arguments from a function into an R function. I normally am able to get this to work just fine by doing !!rlang::sym(argument).

What I'm trying to do is create a function that lets me customize which column in a dataset I want to do a given comparison calculation count on.

For example, I might want to count the number of values equal to 9999 or greater than 5, or maybe less than or equal to 5. This column could change as well.

custom_count=function(dataset, expr){

  result=dataset %>% summarise( sum( !!rlang::sym(expr), na.rm = TRUE)) 
  return(result)
}

custom_count(mtcars, 'mpg > 10')
custom_count( mtcars, 'vs==0')

However, these don't work. Is there anyway for me to pass in this combination of field + comparison sign+ value at the same time?

Upvotes: 0

Views: 983

Answers (2)

moodymudskipper
moodymudskipper

Reputation: 47310

You want to use enexpr because you're passing an expression, not a symbol :

library(dplyr)
custom_count=function(dataset, expr){
  result=dataset %>% summarise( sum( !!rlang::enexpr(expr), na.rm = TRUE)) 
  return(result)
}

custom_count(mtcars, mpg > 10)
#   sum(mpg > 10, na.rm = TRUE)
# 1                          32
custom_count( mtcars, vs==0)
#   sum(vs == 0, na.rm = TRUE)
# 1                         18

Upvotes: 1

Bing
Bing

Reputation: 1103

This seems to work for me.

custom_count=function(dataset, expr){      
  result=dataset %>% summarise( sum( !!expr, na.rm = TRUE)) 
  return(result)
}

custom_count(mtcars, quote(mpg > 10))

Upvotes: 0

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