R help - May 2011 - Flattening lists and environments (was: "how to flatten a list to the same level?")

Dear list,

I came up with a two functions that flatten arbitrary deeply nested 
lists (as long as they're named; not tested for unnamed) and 
environments (see attachment; 'flatten_examples.txt' contains some 
examples).

The paradigm is somewhat similar to that implemented in 'unlist()', yet 
extends it. I would have very much liked to build upon the superfast 
functionality of 'unlist()', but there are some obstacles to this (see 
these two related posts at r-devel from today: 
https://stat.ethz.ch/pipermail/r-devel/2011-May/061070.html and 
https://stat.ethz.ch/pipermail/r-devel/2011-May/061071.html).

Therefore, I had to use a recursive looping paradigm. Yet, if anyone has 
some suggestions on how to speed things up (maybe some Rcpp-people feel 
"called upon"?!? ;-)), I'd appreciate any pointers. Yet I do hope
that
what I came up with is at least of some value for those that posted 
similar questions on how to flexibly flatten nested objects in the past 
(that's why I'm also referring to this older post below; I also build 
upon the code provided by Henrique Dallazuanna and Mark Heckmann).

Best regards,
Janko

PS: Maybe this should rather go into a blog-post, but I don't have one 
yet ;-)

On 19.05.2011 22:16, Janko Thyson wrote:
> From: Mark Heckmann <mark.heckmann_at_gmx.de 
>
<mailto:mark.heckmann_at_gmx.de?Subject=Re:%20[R]%20how%20to%20flatten%20a%20list%20to%20the%20same%20level?>>
>
> Date: Sat, 09 Jan 2010 13:49:15 +0100
>
> Henrique,
>
> thanks for the code!! It works out fine for vectors. I forgot to 
> mention I also have dataframes as list elements. Thus I want the 
> structure of the list element to be kept intact.
>
> I tried an recursive approach (which unfortunately resulted in some 
> more code) which works.
>
> .getNonListElements <- function(x, env){
>
> 	if(class(x)=="list") {
> 		for(i in seq(along=x)) .getNonListElements(x[[i]], env)	# call
> recursively
> 	} else {
> 		res<- get("res", envir = env)		# get res from other env
> 		res<- c(res, list(x))				# add one list element
> 		assign("res", res, envir=env)		# assign back to env
> 	}
>
> }
>
> flattenList <- function(l){
>
> 	res<- list()		  				# make list object
> 	env<- environment()  				# get current env 	
> 	.getNonListElements(l, env)		# search for non list elements recursively
> 	return(res)
>
> }
>
> l <- list(DF=data.frame(A=c(1,2)), vec=c("a", "b"))
l <- list(l,l)
>
> > flattenList(l)
>
> [[1]]
>
>    A
> 1 1
> 2 2
>
> [[2]]
> [1] "a" "b"
>
> [[3]]
>
>    A
> 1 1
> 2 2
>
> [[4]]
> [1] "a" "b"
>
> I am not sure if one can avoid the wrapper function or still use 
> rapply to simplify the code. I do not know how. One more thing I would 
> like to add are the objects names to the generated list. But I did not 
> succeed in that.
>
> Mark
>
> Am 08.01.2010 um 18:29 schrieb Henrique Dallazuanna:
>
> >  Try something about like this:
> >
> >  split(unlist(l), rep(1:length(idx<- rapply(l, length)), idx))
> >
> >  On Fri, Jan 8, 2010 at 1:35 PM, Mark
Heckmann<mark.heckmann_at_gmx.de>
> >  wrote:
> >>  I have a nested list l like:
> >>
> >>  l<- list(A=c(1,2,3), B=c("a", "b"))
> >>  l<- list(l,l, list(l,l))
> >>
> >>  I want the list to be unlisted, but not on the lowest level of
each
> >>  "branch".
> >>  I want the lowest level of each list branch to remain as it is.
> >>  So unlist or unlist(rec=F) do not work here as the level of
nesting
> >>  may
> >>  differ on the elements.
> >>  The result should look like:
> >>
> >>  $A
> >>  [1] 1 2 3
> >>
> >>  $B
> >>  [1] "a" "b"
> >>
> >>  $A
> >>  [1] 1 2 3
> >>
> >>  $B
> >>  [1] "a" "b"
> >>
> >>  $A
> >>  [1] 1 2 3
> >>
> >>  $B
> >>  [1] "a" "b"
> >>
> >>  $A
> >>  [1] 1 2 3
> >>
> >>  $B
> >>  [1] "a" "b"
> >>
> >>  Any ideas?
> >>  TIA!
> >>
> >>  Mark
> >>
> >>
> >> 
------------------------------------------------------------------------------
> >>  Mark Heckmann
> >>  Dipl. Wirt.-Ing. cand. Psych.
> >>  Vorstra?e 93 B01
> >>  28359 Bremen
> >>  Blog:www.markheckmann.de
> >>  R-Blog:http://ryouready.wordpress.com
> >>
> >>  ______________________________________________
> >>  R-help_at_r-project.org mailing list
> >>  https://stat.ethz.ch/mailman/listinfo/r-help
> >>  PLEASE do read the posting
guidehttp://www.R-project.org/posting-guide.html
> >>  and provide commented, minimal, self-contained, reproducible
code.
> >>
> >
> >
> >
> >  -- 
> >  Henrique Dallazuanna
> >  Curitiba-Paran?-Brasil
> >  25? 25' 40" S 49? 16' 22" O
>
>
------------------------------------------------------------------------------
>
> Mark Heckmann
> Dipl. Wirt.-Ing. cand. Psych.
> Vorstra?e 93 B01
> 28359 Bremen
> Blog: www.markheckmann.de
> R-Blog: http://ryouready.wordpress.com
> -- 
> ------------------------------------------------------------------------
>
> *Janko Thyson*
> janko.thyson at ku-eichstaett.de <mailto:janko.thyson at
ku-eichstaett.de>
>
> Catholic University of Eichst?tt-Ingolstadt
> Ingolstadt School of Management
> Statistics and Quantitative Methods
> Auf der Schanz 49
> D-85049 Ingolstadt
>
> www.wfi.edu/lsqm <http://www.wfi.edu/lsqm>
>
> Fon: +49 841 937-1923
> Fax: +49 841 937-1965
>
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-- 
------------------------------------------------------------------------

*Janko Thyson*
janko.thyson at googlemail.com <mailto:janko.thyson at googlemail.com>

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