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I have a question concerning data.table join.

What does the dot does in the following join :

DT1[.(DT2$key),roll=TRUE][,V1]

Both data.tables are key by the column "key".

misha_dodic
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    Same thing as `J` does. Type `?J` to find out more about it. And if both `data.table`'s are keyed, normal syntax is `DT1[DT2, ...]`. – eddi Mar 12 '14 at 15:19
  • [This post](http://stackoverflow.com/questions/22001945/how-is-j-function-implemented-in-the-r-package-data-table/22002174#22002174) may help. – Arun Mar 12 '14 at 15:33

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