[R] Making a factor with common levels ...

[j.logsdon@lancaster.ac.uk]

This is doing my head in.  Staying away from R for too long is bad for the
health!

I have two vectors of character names where there may be repetition and
from which I want to form two factors with the same levels but only if
there are more than N instances of each name in each vector.

I can get the list of common names quite easily, using:

nn<-sort(unique(c(levels(n1)[table(n1)>N],levels(n0)[table(n0)>N])))

Some of the factor levels may be empty for one of the factors but the same
level must be present in the other.

Is there a simple way to extract nn0 and nn1 so that the pairs remain
correctly aligned and each list has at least N cases of each name?  Or do
I have to jump into my steamroller and do a couple of loops?

TIA

John

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