left_join: left_join
In decisionpatterns/data.table.plus: Extensions and Utilities for 'data.table'

Description Usage Arguments Details Examples

implements a default left join for data.table

1 2	## S3 method for class 'data.tableoff' x[i, ...]

`x`	data.table
`i`	object

By convention DT implements DT[X] as a RIGHT JOIN. This convention promotes facts, i.e. the most quickly varying values to be on the RHS of the result. This is anathema to the convention of modeling where the Y's are expressed first. '

 x <- data.table( letters=letters, i=1:26 )
 setkey(x, letters )

 rhs <- data.table( letters=letters[1:5], i=1:5 )
 setkey(rhs, letters )

 data.table:::`[.data.table`(x,rhs)      # RIGHT JOIN

 options( datatable.default.left.join = FALSE )
 x[rhs, on=.(letters)]                     # RIGHT JOIN
 options( datatable.default.left.join = TRUE )
 x[rhs, on=.(letters)]