dcast.data.table eval(fun.aggragate) -- cannot pass as an argument #713
Description
Referred from SO question
Affects 1.9.3 (and not 1.9.2)
TL;DR
If you have a function that calls dcast.data.table, you can't seem to pass fun.aggregate into that call from the function argument.
Because of an eval(fun.aggregate) within dcast.data.table.
Example
I have a table like this:
library(data.table)
t <- data.table(id=rep(1:2, c(3,4)), k=c(rep(letters[1:3], 2), 'c'), v=1:7)
t
id k v
1: 1 a 1
2: 1 b 2
3: 1 c 3
4: 2 a 4
5: 2 b 5
6: 2 c 6
7: 2 c 7 # note the duplicate (2, c)
I reshape to long format, retaining the last occurence of duplicates
dcast.data.table(t, id ~ k, value.var='v', fun.aggregate=last) # last is in data.table
id a b c
1: 1 1 2 3
2: 2 4 5 7
However if I wrap my dcast.data.table call into a function:
f <- function (tbl, fun.aggregate) {
dcast.data.table(tbl, id ~ k, value.var='v', fun.aggregate=fun.aggregate)
}
f(t, last)
Error in `[.data.table`(data, , eval(fun.aggregate), by = c(ff_)) :
could not find function "fun.aggregate"
It looks like the symbol fun.aggregate is being evaluated (eval(fun.aggregate)) and not found (since the function "fun.aggregate" does not exist).
Is there a way to "protect" a function argument from the eval() call when I pass it in (i.e. perhaps this behaviour is intended), or perhaps this is a bug. My personal opinion is that it is a bug, because this works for dcast and not dcast.data.table, and the two should be consistent.