Factor levels.

Rolf Turner wrote:

I have factors with levels ``Unit", "Achieved", and "Scholarship";  
I  wish to replace these with
"U", "A", and "S".

So I do

	fff <- factor(fff,labels=c("U","A","S"))

This works as long as all of the levels are actually present in  
the  factor.  But if ``Scholarship'' is absent
(as if often is) then I get an error.

I can do a workaround such as

	fff <- factor(c("U","A","S")[fff],levels=c("U","A","S"))

but this seems kludgy to me.

Does it even work? (What if it is the first or the 2nd level that  
is absent?

Yes it works.  What's the problem?

	To beat it to death:  if the second level of fff is absent then fff  
will consist entirely of 1's and 3's,
	and so c("U","A","S")[fff] will consist entirely of U's and S's.  I  
can then set the levels to be
	c("U","A","S") and get what I want.

	Note that if I just did

		fff <- factor(c("U","A","S")[fff])

	in these circumstances, then I would get a factor whose levels were c 
("U","S") which is NOT what I want.
	(I.e. I want the levels always to be c("U","A","S") irrespective of  
what levels are actually present in the factor.)

The canonical way is

factor(fff, levels=c("Unit", "Achieved", "Scholarship"), labels=c 
("U","A","S"))

Right.  That is indeed sexier.  Thanks.

			cheers,

				Rolf

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