How to pass a column name as a function parameter to a dplyr function in R.

If you need to pass a column name as a function parameter to a dplyr function/verb such as filter() or mutate() do this:

library(dplyr)

## Make a dummy dataframe
country<-c("USA", "Mexico", "Canada", "USA", "Mexico", "Canada", "USA", "Mexico")
fruits<-c("apple", "banana", "apple", "banana", "orange", "orange", "apple", "banana")
weight<-c(10,20,4,20,11,15,25,23)

df<-data.frame(fruits, country, weight)

## Write function that filters a column name by value.
filter_fruit<-function(x, col_name=fruits, value="apple"){
  x%>%
    filter({{col_name}} ==value)
}

And calling the function:

r$> filter_fruit(df)
  fruits country weight
1  apple     USA     10
2  apple  Canada      4
3  apple     USA     25

r$> filter_fruit(df, col_name=country, value="USA")
  fruits country weight
1  apple     USA     10
2 banana     USA     20
3  apple     USA     25

r$> filter_fruit(df, col_name=weight, value=20)
  fruits country weight
1 banana  Mexico     20
2 banana     USA     20

The key is the {{_}} around the column name and not adding quotes around the function parameter defaults when writing the function.

You can find more information in the Tidyverse Documentation.