You want this?

> basicSubMean <- aggregate(basicSub[c("score")], by=list(basicSub$student),
FUN=mean, na.rm=TRUE)
> basicSubMean
  Group.1 score
1       1  55.0
2       2  60.0
3       3  67.5

bests
milton

On Sun, Jan 3, 2010 at 10:46 PM, david hilton shanabrook <
dhshanab@acad.umass.edu> wrote:

> I want to use aggregate with the mean function on specific columns
>
> gender <- factor(c("m", "m", "f", "f", "m"))
> student <- c(0001, 0002, 0003, 0003, 0001)
> score <- c(50, 60, 70, 65, 60)
> basicSub <- data.frame(student, gender, score)
> basicSubMean <- aggregate(basicSub, by=list(basicSub$student), FUN=mean,
> na.rm=TRUE)
>
> This doesn't work, one cannot take the mean of a factor (gender).  Is there
> any way of specifying which columns to use for the mean?  I want to
> aggregate by student, obtaining mean scores, and assume any other factors
> are unchanging in a specific student, ie. gender.
>
> Thanks
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>
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