DT=data.table(a=1:2, b=3:4)
DT[, f(b), by=a, env=list(f=sum)]
# Error in as.character(jsub[[1L]]) :
# cannot coerce type 'builtin' to vector of type 'character'
The issue is that the resulting query, instead of being DT[, sum(b), by=a], becomes DT[, .Primitive("sum")(b), by=a].
The same will happen for any closure:
DT[, f(b), by=a, env=list(f=\(x) sum(x))]
# Error in as.character(jsub[[1L]]) :
# cannot coerce type 'closure' to vector of type 'character'
This is not a general issue with [:
DT[, .Primitive("sum")(b), by=a]
# a V1
# <int> <int>
# 1: 1 3
# 2: 2 4Reactions are currently unavailable
The issue is that the resulting query, instead of being DT[, sum(b), by=a], becomes DT[, .Primitive("sum")(b), by=a].
The same will happen for any closure:
This is not a general issue with [: