Hi
I have a problem in R that I have been trying to solve but without 
success.
I am trying to join two tables on two variables : an ID and a date 
(optional) that will be common between the two tables

In SQL (and SAS PROC SQL) I am a frequent user of the "select" command and 
I am used to the following nomenclature : 

select a.*, b.c, b.y, b.z from table1 a, table2 b where a.date=b.date and 
a.id=b.id

I tried this in R (using sqldf) but it takes waaaay too long to get the 
result. My data sets are >1 gb each.
Is there any way this can be done by merge() or any other more "R-like" 
way ? 
I have tried making a compound variable with paste(id, as.character(date), 
sep="") and merge() on that but since the date more often than not is NA
this doesnt seem to work. I'm a bit stuck and the documentation is of 
little help to me in this case. 
If anybody would be kind to point me in the right direction I would be 
grateful.

Jan


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