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.
As we are passing character elements, it would be better to convert to sym
bol 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