I am trying write a function which creates a new column by multiplying two other columns, with the names of all three columns being given as (string) parameters to the function.
I was thinking I could write something like this:
A <- data.frame(x = 1:5, y = 11:15)
f <- function(x, y, new) {
x_quo <- rlang::enquo(x)
y_quo <- rlang::enquo(y)
new_quo <- rlang::enquo(new)
A %<>% mutate (!!new_quo := !!x_quo * !!y_quo)
A
}
f("x", "y", "new")
I was expecting this to be equivalent to running this code:
A <- data.frame(x = 1:5, y = 11:15)
A %<>% mutate (new = x * y);
However, but when I run that first code, I get this error:
Error: Problem with `mutate()` input `new`.
x non-numeric argument to binary operator
i Input `new` is `"x" * "y"`.
Run `rlang::last_error()` to see where the error occurred.
What does this error mean? Is there a way to create a function like I've described?
Try to use sym and evaluate it with !!. I would also pass additional data argument to the function.
library(dplyr)
library(rlang)
f <- function(data, x, y, new) {
data %>% mutate (!!new := !!sym(x) * !!sym(y))
}
A %>% f("x", "y", "new")
# x y new
#1 1 11 11
#2 2 12 24
#3 3 13 39
#4 4 14 56
#5 5 15 75
identical(A %>% f("x", "y", "new"), A %>% mutate (new = x * y))
#[1] TRUE