
Hi Gurus:
 
If I have a large dataset of the form of:
 
> x <- data.frame(V1 = runif(10), V2 = sample(c('A','B','C'),10,T)) > x          V1 V21  0.2691580  A2  0.8711267  B3  0.2674728  C4  0.3278876  A5  0.1809152  A6  0.2499651  C7  0.9155174  A8  0.8004974  B9  0.7885516  A10 0.9301630  A
And I want a V3 that =V2 if V2=A, and =D if V2=B or C. In other words I want to use a vectorized way to combine some levels, rather than having to loop through a large dataset.
 
Similarly, if I want to group V1 into levels, what is a fast way to do it?
 
Thank you!
Karen
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