R help - Feb 2010 - Error in tapply when reordering levels of a factor

I have this
> grades$grade
...
[4009] A  B  A- A- A- B+ A  A- B+ B  A  B  B  B  A  A- A  A- A- B+ A- A  A  B+
[4033] A- A- A- A  A- B  A  A  A- A
Levels: A A- A+ B B- B+ C  C+

I want to change the order of the levels
>
reorder(grades$grade,c('A+','A','A-','B+','B','B-','C+','C'))
Error in tapply(X, x, FUN, ...) : arguments must have same length

What am I doing wrong? Thanks

Tom

On Feb 27, 2010, at 10:01 PM, Thomas Levine wrote:
> I have this
>
>> grades$grade
> ...
> [4009] A  B  A- A- A- B+ A  A- B+ B  A  B  B  B  A  A- A  A- A- B+  
> A- A  A  B+
> [4033] A- A- A- A  A- B  A  A  A- A
> Levels: A A- A+ B B- B+ C  C+
>
> I want to change the order of the levels
>
>> reorder(grades$grade,)
Try instead:

grades$grades <- factor(grades$grades,
                  levels=
c('A+','A','A-','B+','B','B-','C+','C')
> Error in tapply(X, x, FUN, ...) : arguments must have same length
>
> What am I doing wrong? Thanks
>
> Tom
>
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