[R] Replacing variables in one dataset with those from another

[mcginnis21]

Hoping someone out there can help me...this seems like an easy task but I
can't figure it out...

I want to replace variables in one dataset (Dataset1) with a variable from
another dataset (Dataset2). 
All the values for variables x1 and x2 in Dataset1 have a unique match to
the variable uniquenum in Dataset2.  For example, in Dataset1 grpnum A has a
value of 343 for variable x1.  In Dataset2, 343 will only be found once for
variable uniquenum.  I would like to create a new dataset where the variable
x1 from Dataset1 will be replaced by uniqueid from Dataset2.  So variable x1
for grpnum A now would equal GHU82RK02HD7D6 rather than 343.   Below is an
abbreviated example from my datasets to show what I’m trying to do rather
than explain in words because I’m not sure my question is coming across very
clearly.   I have about 100 columns in Dataset1 (x1, x2, etc.) and the
variable uniquenum in Dataset2 has about 4,000 values.

Dataset1
grpnum	x1	x2
A	343	334
B	313	898
C	4076	4077
D	275	276

Dataset2
unique num	uniqueid
343	GHU82RK02HD7D6
4076	GHU82RK02IXPC7
4077	GHU82RK02HICZ2
261	GHU82RK02FLOFU
4100	GHU82RK02IDO7K
4101	GHU82RK02HQYQL
4102	GHU82RK02GADV1
4103	GHU82RK02G7RQH
4104	GHU82RK02HQD2E



NewDataset
grpnum	x1	x2
a	GHU82RK02HD7D6	  Na
b	Na	Na
c	GHU82RK02IXPC7	GHU82RK02HICZ2
d	Na	Na



Thanks for your time and thoughts.  I hope someone can help!



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