[R] apply for nested lists

[Berton Gunter]

apply() statements **are** disguised loops and therefore are **not**
necessarily more efficient than explicit looping. Their principal advantage
is usually code readability. 

As another readability issue, note that x[[i]][[j]][[k]] can be abbreviated
to x[[c(i,j,k]].

I leave to others the pleasure of deciphering and improving your code,
however. 

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of 
> Alexandre Sanchez Pla
> Sent: Wednesday, January 26, 2005 8:50 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] apply for nested lists
> 
> Hi,
> 
> I am working with lists whose terms are lists whose terms are 
> lists. Although 
> the real ones contain locuslink identifiers and GO 
> annotations (I work with the 
> Bioconductor GO) package, I have prepared an simplified 
> example of what I have 
> and what I would like to do with it:
> 
> Imagine I have a list such as:
> 
> tst.list<-list("1"=list("1A"=list(ID="1A",VAL=172),"1B"=list
> (ID="1B",VAL=134),"1C"=list(ID="1C",VAL=0)),"2"=list("2A"=NA),
> "3"=list("3A"=list
> (ID="3A",VAL=33),"3B"=list(ID="3B",VAL=2)))
> 
> I would like, for instance, to be able to extract some values 
> such as the 
> content of the "VAL" field, which may sometimes not be available.
> I may do it using a nested for such as:
> 
> x<-character(0)
> for (i in 1:length(tst.list)){
>     if (!is.na(tst.list[[i]][[1]][[1]])){
>         for (j in 1:length(tst.list[[i]]))
>             {x<-c(x,tst.list[[i]][[j]]$VAL)}}
>     else    
>             {x<-c(x, NA)}}
> 
> which gives me what I need
> 
> > x
> [1] "172" "134" "0"   NA  "33"  "2"  
> 
> According to most R documents this may be done more 
> efficiently using apply 
> instructions, but I have failed in my temptatives to obtain the same
> 
> Thanks for any help.
> 
> Alex
> 
> 
> -- 
> Dr.Alex Sánchez
> Departament d'Estadística.
> Universitat de Barcelona
> asanchez at ub.edu
> 
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