[R] Newbie question: Statistical functions (e.g., mean, sd) in a "transform" statement?

[Gabor Grothendieck]

Try this using the builtin data set anscombe:

transform(anscombe, rowMeans = rowMeans(anscombe))

On 1/19/07, Ben Fairbank <BEN at ssanet.com> wrote:
> Greetings listeRs -
>
>
>
> Given a data frame such as
>
>
>
> times
>
>       time1    time2     time3    time4
>
> 1  70.408543 48.92378  7.399605 95.93050
>
> 2  17.231940 27.48530 82.962916 10.20619
>
> 3  20.279220 10.33575 66.209290 30.71846
>
> 4         NA 53.31993 12.398237 35.65782
>
> 5   9.295965       NA 48.929201       NA
>
> 6  63.966518 42.16304  1.777342       NA
>
>
>
> one can use "transform" to total all or some columns, thus,
>
>
>
> times2 <- transform(times,totaltime=time1+time2+time3+time4)
>
>
>
> > times2
>
>       time1    time2     time3    time4 totaltime
>
> 1  70.408543 48.92378  7.399605 95.93050  222.6624
>
> 2  17.231940 27.48530 82.962916 10.20619  137.8863
>
> 3  20.279220 10.33575 66.209290 30.71846  127.5427
>
> 4         NA 53.31993 12.398237 35.65782        NA
>
> 5   9.295965       NA 48.929201       NA        NA
>
> 6  63.966518 42.16304  1.777342       NA        NA
>
>
>
> I cannot, however, find a way, other than "for" looping,
>
> to use statistical functions, such as mean or sd, to
>
> compute the new column.  For example,
>
>
>
> >
> times2<-transform(times,meantime=(mean(c(time1,time2,time3,time4),na.rm=
> TRUE)))
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>
>
> > times2
>
>
>
>  time1    time2     time3    time4 meantime
>
> 1  70.408543 48.92378  7.399605 95.93050 45.54178
>
> 2  17.231940 27.48530 82.962916 10.20619 45.54178
>
> 3  20.279220 10.33575 66.209290 30.71846 45.54178
>
> 4         NA 53.31993 12.398237 35.65782 45.54178
>
> 5   9.295965       NA 48.929201       NA 45.54178
>
> 6  63.966518 42.16304  1.777342       NA 45.54178
>
>
>
> How can this be done?  And, generally, what is the recommended method
>
> for creating computed new columns in data frames when "for" loops take
>
> too long?
>
>
>
> With thanks for any suggestions,
>
>
>
> Ben Fairbank
>
>
>
> Using version 2.4.1 on a Windows XP professional operating system.
>
>
>
>
>        [[alternative HTML version deleted]]
>
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