data.table.joins.R

gistfile1.txt

# samples of some joins of data.tables with trivial tables


library(data.table)
dt1 <- data.table(f1=1:5, f2=sample(letters,5))
dt2 <- data.table(f1=2:6, f3=sample(letters,5))
dt3 <- data.table(f1=c(2,2:6), f3=sample(letters,6))
dt1
dt2
dt3

#inner join
merge(dt1, dt2, by="f1")

#left join
dt1[dt2,on="f1==f1",`:=`(f3=i.f3)]
dt1

#left join - note no duplication and new calculated field
dt1 <- data.table(f1=1:5, f2=sample(letters,5))
dt1[dt3,on="f1==f1",`:=`(f3=i.f3, f4=paste0(f2,i.f3))]
dt1

# outer  join
merge(dt1, dt2, by="f1", all=TRUE)

# right join
dt1 <- data.table(f1=1:5, f2=sample(letters,5))
dt2[dt1,on="f1==f1"]