[R] get level combinations from "by" list

[Dimitris Rizopoulos]

I think these are not stored by "by()" and they are produced inside 
"print.by()". One way to get them could be:

dn <- dimnames(grouped)
dn <- expand.grid(dn)
dn <- dn[!sapply(grouped[1:nrow(dn)], is.null), ]
dn

rownames(dfr) <- apply(dn, 1, paste, collapse = "-")
dfr


I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat/
     http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm


----- Original Message ----- 
From: "bogdan romocea" <br44114 at gmail.com>
To: <R-help at stat.math.ethz.ch>
Sent: Wednesday, June 08, 2005 4:56 PM
Subject: [R] get level combinations from "by" list


> Dear useRs,
>
> Given this code I end up with a list of class "by":
>
> a <- sample(1:5,200,replace=TRUE)
> b <- sample(c("v1","v2","v3"),200,replace=TRUE)
> c <- sample(c(11,22,33),200,replace=TRUE)
> data <- runif(200)
> grouped <- by(data,list(a,b,c),function(x) {c(min=min(x),max=max(x),
> median=round(median(x),digits=2),mean=round(mean(x),digits=2))})
> dfr <- do.call("rbind",grouped)    #the levels are missing
> #----------
> grouped
> typeof(grouped)
> class(grouped)
> dimnames(grouped)
>
> How do I get at the levels of the 'group by' variables for each
> subset? For example, from this part of the "by" list I want 4, v2 
> and
> 33:
> : 4
> : v2
> : 33
>      min       max    median      mean
> 0.3897450 0.9215315 0.7300000 0.6700000
> ---------------------------------------
>
> Thank you,
> b.
>
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