Pass column name as parameter to a function using dplyr

An R function with a parameter that accepts a data.frame column can’t evaluate the column argument until it is first ‘quoted’, followed by an ‘unquote’ within the dyplr function.

‘Quote’ a column using enquo(), then ‘unquote’ it using !!.

Try it

library(dplyr)
# build example data.frame
id <-c(1,2,3,4,5,6)
value <- c('a','b','b','c','c','c')
df <- data.frame(id, value)

# create function to count data.frame column values
my_function <- function(data, col) {
    col <- enquo(col)            # quote
    data %>%
        group_by(!!col) %>%      # unquote
        summarise(count = n())
}

# call function, passing data.frame and column 
my_function(df, value)

# A tibble: 3 x 2
  value count
  <fct> <int>
1 a         1
2 b         2
3 c         3

Of course, you could enquo() the column as it’s passed to the function. Personally, I like to keep function calls cleaner by performing function-required manipulations on arguments within the function itself.

my_function <- function(data, col) {
    data %>%
        group_by(!!col) %>%      # unquote
        summarise(count = n())
}

# call function with column 'quoted'
my_function(df, enquo(value))    # quote

# A tibble: 3 x 2
  value count
  <fct> <int>
1 a         1
2 b         2
3 c         3

Reference

https://dplyr.tidyverse.org/articles/programming.html