On 6/7/2012 12:46 PM, Juliet Hannah wrote:
Hi Yike,
In Matthew's email, he writes:
So in other words, when i has no key it's the first column of i to the
first column of x's key, the 2nd column of i to the 2nd column of x's key,
etc.
Right, I figured that was the part which was supposed to answer the
question, however the language is ambiguous in Matt's reply, which is
why I asked for clarification. If what you're saying is the case, then
what the docs should say is something along the lines of...
"If i is not keyed, then data.table performs a join on a positional
match between the columns of i and the keys of X. In other words, a join
is performed on (column 1 of i, column 1 of key of X, then column 2 of
i, column 2 of key of X, etc...)"
Don't have to use my wording, but the original was ambiguous to me.
Cheers,
Yike
I think this answers my original question. In the example (which is
from the FAQ), i has no key. So it seems
the *default* is to match the first column of i to x's key.
That's how data.table "knows". It uses the first column as default.
At least that's the way I understand things now. Matthew, please
correct if I've misunderstood.
Regards,
Juliet
i-bin/mailman/listinfo/datatable-help
_______________________________________________
datatable-help mailing list
[email protected]
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
