[R] Question about many-to-one merge

hongwei awaypku at gmail.com
Wed Jan 20 23:37:36 CET 2010


I have spent a whole afternoon searching for the solution, but got nothing so
far. It should be a simple problem.
I have two datasets to merge. The first one just contains two ID columns and
it looks like:

FromID  ToID
1           2
1           3
2           1
2           3
3           1
3           2

The second one contains a ID column and a variable:
ID      X
1       100
2       150
3       130

What I want is to merge the two datasets together using the ToID and ID. The
final merged dataset should look like:

FromID   ToID   X
1            2      150
1            3      130
2            1      100
2            3      130
3            1      100
3            2      150

The Merge command doesn't work well. I also don't want to use for loop. I
feel that there must be some subscripting or other tricks to use, but I
couldn't figure it out.

Any help is appreciated!!

-Hongwei

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