[R] Subtraction with aggregate

[Jim Lemon]

Hi Gang,
This is one way:

gangdat<-read.table(text="subject   QM    emotion     yi
  s1   75.1017   neutral  -75.928276
  s2  -47.3512   neutral -178.295990
  s3  -68.9016   neutral -134.753906
  s1   17.2099  negative -104.168312
  s2  -53.1114  negative -182.373474
  s3  -33.0322  negative -137.420410",
 header=TRUE)
library(prettyR)
gangstretch<-stretch_df(gangdat,"subject",c("emotion","yi"))
gangstretch$emodiff<-gangstretch$yi_2-gangstretch$yi_1
gangstretch$emodiff

Jim


On Fri, Jul 29, 2016 at 6:40 AM, Gang Chen <gangchen6 at gmail.com> wrote:
> With the following data in data.frame:
>
> subject   QM    emotion     yi
>   s1   75.1017   neutral  -75.928276
>   s2  -47.3512   neutral -178.295990
>   s3  -68.9016   neutral -134.753906
>   s1   17.2099  negative -104.168312
>   s2  -53.1114  negative -182.373474
>   s3  -33.0322  negative -137.420410
>
> I can obtain the average between the two emotions with
>
> mydata <- read.table('clipboard', header=TRUE)
> aggregate(mydata[,c('yi', 'QM')], by=list(subject=mydata$subject), mean)
>
> My question is, what is a nice way to get the difference between the
> two emotions?
>
> Thanks,
> Gang
>
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