r - Left join using data.table

Suppose I have two data.table's:

A:

  A  B

1: 1 12
2: 2 13
3: 3 14
4: 4 15

B:

   A  B
1: 2 13

2: 3 14

and I have the following code:

merge_test = merge(dataA, dataB, by="A", all.data=TRUE)

I get:

   A B.x B.y
1: 2  13  13
2: 3  14  14

However, I want all the rows in dataA in the final merged table. Is there a way to do this?

Answer

You can try this:

# used data

# set the key in 'B' to the column which you use to join
A <- data.table(a = 1:4, b = 12:15)
B <- data.table(a = 2:3, b = 13:14, key = 'a') 

B[A]