[R] summarizing a dataset on a factor

[Tom Wright]

Thanks David,
Neat use of merge there.

I think I can also do this with:

ddply(data,.(id),f)

On Thu, 2014-03-27 at 16:06 -0500, David Carlson wrote:
> It may be possible to do this in a single step, but
> 
> > x1 <- aggregate(response~id+age, data, mean)
> > x2 <- data[data$eye=="l", c("id", "response2")]
> > merge(x1, x2)
>   id age response response2
> 1  1   2     4.60      High
> 2  2   9     2.65      High
> 3  3   5     3.65      High
> 4  4   2     7.55      High
> 5  5  11     4.15      High
> 
> -------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
> 
> -----Original Message-----
> From: r-help-bounces at r-project.org
> [mailto:r-help-bounces at r-project.org] On Behalf Of Tom Wright
> Sent: Thursday, March 27, 2014 3:48 PM
> To: r-help at r-project.org
> Subject: [R] summarizing a dataset on a factor
> 
> Hi all,
> I've spent too long in matlab land recently and seem to have
> forgotten
> my R skillz ;-)
> I'm sure I'm missing a simple way to do this...
> 
> Given a data frame
> id<-rep(1:5,2)
> eye<-c(rep('l',5),rep('r',5))
> age<-rep(round(runif(5,0,12)),2)
> response<-round(runif(10,1,10)*10)/10
> response2<-sample(c('High','Low'),10,replace=TRUE)
> 
> data<-data.frame(id,eye,age,response,response2)
> 
> I want to create a new dataset averaging the response variable
> from both
> eyes for each test.
> 
> I know there are many ways to do this but... I would also like
> to keep
> the value of the response2 variable for the left eye.
> 
> ending up with the dataset
> id	age	response	response2
> 1	9	3.65	High
> 2	10	3.85	High
> 3	8	8.15	Low
> 4	4	4.4	Low
> 5	0	4.6	High
> 
> I thought something like
> f<-function(x){#make my choices here}
> aggregate(data,list(data$id),f)
> 
> but x only seems to contain the first column of data.
> 
> I could probably have done this manually in the time spent
> writing this
> email.
> any help appreciated, 
> Tom
> 
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