Running aggregate function within dmapply (ddR package) - r

Question

I would like to run the aggregate function within the dmapply function as offered through the ddR package.
Desired results
The desired results reflect a simple output generated via aggregate in base:
aggregate(
x = mtcars$mpg,
FUN = function(x) {
mean(x, na.rm = TRUE)
},
by = list(trans = mtcars$am)
)
which produces:
trans x
1 0 17.14737
2 1 24.39231
Attempt - ddmapply
I would like to arrive at the same results while utilising ddmapply, as attempted below:
# ddR
require(ddR)
# ddR object creation
distMtcars <- as.dframe(mtcars)
# Aggregate / ddmapply
dmapply(
FUN = function(x, y) {
aggregate(FUN = mean(x, na.rm = TRUE),
x = x,
by = list(trans = y))
},
distMtcars$mpg,
y = distMtcars$am,
output.type = "dframe",
combine = "rbind"
)
The code fails:
Error in match.fun(FUN) : 'mean(x, na.rm = TRUE)' is not a
function, character or symbol Called from: match.fun(FUN)
Updates
Fixing error pointed out by #Mike removes the error, however, does not produce the desired result. The code:
# Avoid namespace conflict with other packages
ddR::collect(
dmapply(
FUN = function(x, y) {
aggregate(
FUN = function(x) {
mean(x, na.rm = TRUE)
},
x = x,
by = list(trans = y)
)
},
distMtcars$mpg,
y = distMtcars$am,
output.type = "dframe",
combine = "rbind"
)
)
yields:
[1] trans x
<0 rows> (or 0-length row.names)

Answer 1

It works fine for me if you change your aggregate function to be consistent with the one you call earlier: FUN = function(x) mean(x, na.rm = T). The reason it can't find mean(x, na.rm = T) is because it isn't a function (it's a function call), rather mean is a function.
Also it will give you NA results unless you change your x = distMtcars$mpg to x = collect(distMtcars)$mpg. Same for y. With all that said, I think this should work for you:
res <-dmapply(
FUN = function(x, y) {
aggregate(FUN = function(x) mean(x, na.rm = TRUE),
x = x,
by = list(trans = y))
},
x = list(collect(distMtcars)$mpg),
y = list(collect(distMtcars)$am),
output.type = "dframe",
combine = "rbind"
)
Then you can do collect(res) to see the result.
collect(res)
# trans x
#1 0 17.14737
#2 1 24.39231