[R] Error in tapply when reordering levels of a factor

[David Winsemius]

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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David Winsemius, MD
Heritage Laboratories
West Hartford, CT