Question

Possible Duplicate:
Select NA in a data.table in R

just wondering if this is an intended feature or a bug in data.table?

a = data.frame(a=c(NA,1),aa=c(0,11))
b = data.frame(a=c(1),bb=c(11))
merge(a,b,all.x=T,by="a")
   a aa bb
1  1 11 11
2 NA  0 NA

a = data.table(a=c(NA,1),aa=c(0,11))
b = data.table(a=c(1),bb=c(11))
merge(a,b,all.x=T,by="a")
    a aa bb
1: NA  0 11
2:  1 11 11

same again this way

setkey(b,a)
b[a]
    a bb aa
1: NA 11  0
2:  1 11 11

I’d really expect the behaviour you get with data.frame this case.

thansk

Answer 1

See FR#1043 Allow or disallow NA in keys?..

It is a known issue, NA values are allowed, but you can’t join with them.

See the duplicate question and answer Select NA in a data.table in R for a more detailed description