[R] paste together object names to pass it on to a function

Patrick Burns pburns at pburns.seanet.com
Fri Jan 30 18:35:17 CET 2009

A rule of thumb is that if the solution seems a lot
harder than the task, there is probably a better
approach.  I think you want something like:

lapply(gnuff[nam], function(x) x$LE)

Patrick Burns
patrick at burns-stat.com
+44 (0)20 8525 0696
(home of "The R Inferno" and "A Guide for the Unwilling S User")

stefan.duke at gmail.com wrote:
> Hello,
> I have a maybe trivial question, but I simply don't understand well
> enought how to work with text/strings:
> I have a rather compelx data structure, a big list with several
> sub-lists/dataframes and for certain calculations  (which I do in
> loops), I only need a certain group of  sub-lists/dataframes, which I
> want to specify with a name vector and paste together the object name
> and pass it on to a function.
> Here an (hopefully) instructive example
> #Data Example
> gnuff<-list()
> gnuff$IHD$LE<-66
> gnuff$LUNG$LE <-55
> #This is the list, where I collect data for different diseases at the
> second level of the list
> #Now I want to do calcualtions just for these two diseases and the
> sub-list "LE" within these diseases
> nam <- c("LUNG","IHD")
> for(i in 1:2)
> x[i] <- paste("gnuff",nam[i],"LE",sep="$") /2
> x
> #So I try to paste the name of the object which I mean
> (gnuff$IHD$LEand gnuff$LUNG$LE, respectivly), but R treats them as a
> string and not as the name of an object.
> # I tried seveal commands to make it treat like an object name (the
> get() looked most promising), but so far to no avail
> #commands I have tried
> j <- eval(paste("gnuff",nam[i],"LE",sep="$"))
> parse(paste("gnuff",nam[i],sep="$"))
> quote(paste("gnuff",nam[i],sep="$"))
> get(paste("gnuff",nam[i],sep="$"))
> Anybody any hints where to look?
> Thanks and have a great weekend!
> Best,
> Stefan
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