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

[Gavin Simpson]

On Fri, 2007-01-19 at 11:54 -0600, Ben Fairbank wrote:
> Greetings listeRs - 

Here are two solutions, depending on whether you wanted the NA's or not,
and I assume you wanted the row means:

> times3 <- transform(times, meantime = rowMeans(times))
> times3
      time1    time2     time3    time4 meantime
1 70.408543 48.92378  7.399605 95.93050 55.66561
2 17.231940 27.48530 82.962916 10.20619 34.47159
3 20.279220 10.33575 66.209290 30.71846 31.88568
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
> times4 <- transform(times, meantime = rowMeans(times, na.rm = TRUE))
> times4
      time1    time2     time3    time4 meantime
1 70.408543 48.92378  7.399605 95.93050 55.66561
2 17.231940 27.48530 82.962916 10.20619 34.47159
3 20.279220 10.33575 66.209290 30.71846 31.88568
4        NA 53.31993 12.398237 35.65782 33.79200
5  9.295965       NA 48.929201       NA 29.11258
6 63.966518 42.16304  1.777342       NA 35.96897

HTH

G

> 
> 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)))
> 
>  
> 
> > 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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