Subsetting a data.table using another data.table

Question

I have the dt and dt1 data.tables.

dt<-data.table(id=c(rep(2, 3), rep(4, 2)), year=c(2005:2007, 2005:2006), event=         


        

Answer 1

Use merge:

merge(dt,dt1, by=c("year","id"))
   year id event performance
1: 2005  2     1        1000
2: 2006  2     0        1001
3: 2007  2     0        1002

Answer 2

setkeyv(dt,c('id','year'))
setkeyv(dt1,c('id','year'))
dt[dt1,nomatch=0]

Output -

> dt[dt1,nomatch=0]
   id year event performance
1:  2 2005     1        1000
2:  2 2006     0        1001
3:  2 2007     0        1002