I try to write a simple function wrapping around the purrr::pmap_dbl() function.
I have the following data:
df <- data.frame(
col1 = 1:5,
col2 = 2:6,
col3 = 3:7
)
And the following function:
addfn <- function(x, y){
x^2 + y
}
Then I would like to write a function like:
testfn <- function(data, a, b){
purrr::pmap_dbl(data, function(a, b, ...) addfn(a, b))
}
Unfortunately, testfn(df, col1, col2) gives an error in this case. I would like to obtain the same output as the output obtained by:
purrr::pmap_dbl(df, function(col1, col2, ...) addfn(col1, col2))
What is the way to do this?
1) testfn First, note that using testfn from the question that this already works:
testfn(unname(df[c("col1", "col3")]))
## [1] 4 8 14 22 32
2) testfn2 and we can modify that to:
testfn2 <- function(data, ...) {
data %>% select(...) %>% unname %>% purrr::pmap_dbl(addfn)
}
testfn2(df, col1, col3)
## [1] 4 8 14 22 32
testfn2(df, "col1", "col3")
## [1] 4 8 14 22 32
3) base R Of course as has been pointed out we don't really need purrr for this. This works in base R because addfn is vectorized:
with(df, addfn(col1, col3))
## [1] 4 8 14 22 32
or if addfn were not vectorized then:
with(df, mapply(addfn, col1, col3))
## [1] 4 8 14 22 32
and we could write this function using standard evaluation:
testfn3 <- function(data, a, b) mapply(addfn, df[[a]], df[[b]])
testfn3(df, "col1", "col3")
## [1] 4 8 14 22 32
or using non-standard evaluation:
testfn4 <- function(data, ...) eval.parent(substitute(
with(data, mapply(addfn, ...))
))
testfn4(df, col1, col3)
## [1] 4 8 14 22 32