i want to write a custom function with tidyverse verbs/syntax that accepts the grouping parameters of my function as string

Question

I want to write a function that has as parameters a data set, a variable to be grouped, and another parameter to be filtered. I want to write the function in such a way that I can afterwards apply map() to it and pass the variables to be grouped in to map() as a vector. Nevertheless, I don't know how my custom function rating() accepts the variables to be grouped as a string. This is what i have tried.

    data = tibble(a = seq.int(1:10), 
                  g1 = c(rep("blue", 3), rep("green", 3), rep("red", 4)), 
                  g2 = c(rep("pink", 2), rep("hotpink", 6), rep("firebrick", 2)),
                  na = NA, 
                  stat=c(23,43,53,2,43,18,54,94,43,87)) 
    
    rating = function(data, by, no){
      data %>%
        select(a, {{by}}, stat) %>%
        group_by({{by}}) %>%
        mutate(rank = rank(stat)) %>%
        ungroup() %>%
        filter(a == no)
    }
    
    fn(data = data, by = g2, no = 5) #this works

And this is the way i want to use my function


map(.x = c("g1", "g2"), .f = ~rating(data = data, by = .x, no = 1))

... but i get


Error: Must group by variables found in `.data`.
* Column `.x` is not found.

score 1 · Accepted Answer · answered Feb 16 '22 at 19:07

As we are passing character elements, it would be better to convert to symbol and evaluate (!!)

library(dplyr)
library(purrr)
rating <- function(data, by, no){
      by <- rlang::ensym(by)
      data %>%
        select(a, !! by, stat) %>%
        group_by(!!by) %>%
        mutate(rank = rank(stat)) %>%
        ungroup() %>%
        filter(a == no)
    }

-testing

> map(.x = c("g1", "g2"), .f = ~rating(data = data, by = !!.x, no = 1))
[[1]]
# A tibble: 1 × 4
      a g1     stat  rank
  <int> <chr> <dbl> <dbl>
1     1 blue     23     1

[[2]]
# A tibble: 1 × 4
      a g2     stat  rank
  <int> <chr> <dbl> <dbl>
1     1 pink     23     1

It also works with unquoted input

> rating(data, by = g2, no = 5)
# A tibble: 1 × 4
      a g2       stat  rank
  <int> <chr>   <dbl> <dbl>
1     5 hotpink    43     3

i want to write a custom function with tidyverse verbs/syntax that accepts the grouping parameters of my function as string

1 Answers1