R Data.Table: In-memory left join multiple columns from left and right side -


i want merge 2 data tables on multiple columns using data table. 

## 2 tables <- data.table(a = 1:4, b = 12:15, c = 10:13)     b  c 1: 1 12 10 2: 2 13 11 3: 3 14 12 4: 4 15 13  b <- data.table(a = 1:3, b = 12:14, d = 10:12, e = 10:12)     b  d  e 1: 1 12 10 10 2: 2 13 11 11 3: 3 14 12 12

i result:

a <- merge(a, b, = c('a', 'b'), all.x = t)     b  c  d  e 1: 1 12 10 10 10 2: 2 13 11 11 11 3: 3 14 12 12 12 4: 4 15 13 na na

this answer showed data table can edit data frame in-memory, it's more efficient when using large data sets. code suggested is

a[b, bb:=i.b, on='a']

how can alter code data frame merged in-memory, , result same above?

if meant join. here i.d or i.e not needed columns unique in 'b'

nm1 <- setdiff(names(b), names(a))  a[b, (nm1) :=  mget(nm1), on = .(a, b)] #    b  c  d  e #1: 1 12 10 10 10 #2: 2 13 11 11 11 #3: 3 14 12 12 12 #4: 4 15 13 na na

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