[R] why "object 'x' not found"?

[Andrew Robinson]

Thanks, Bill.

Andrew

On Thu, Feb 07, 2013 at 09:21:53PM +0000, William Dunlap wrote:
> >> Notice that the '[[' function is superior in every way to the '$' function. 
> > I'm curious to know whether you can point to some consolidated comparison?
> 
> Two problems are that List$name allows abbreviations of name and does not allow
> variable names.
> 
> With List$name you get:
>   > List <- list(Eleven=11, Twelve="xii")
>   > str(List)
>   List of 2
>    $ Eleven: num 11
>    $ Twelve: chr "xii"
>   > List$E # $ accepts abbreviations, which might seem nice
>   [1] 11
>   > List$E <- List$E + 100 # but can bite you in replacements
>   > str(List) # Eleven not incremented, new E created
>   List of 3
>    $ Eleven: num 11
>    $ Twelve: chr "xii"
>    $ E     : num 111
>   > nm <- "Twelve" # want to use component named variable
>   > List$nm  # no component named "nm"
>   NULL
>   > eval(parse(text=paste0("List", "$", nm))) # ugly dangerous hack
>   [1] "xii"
>   > eval(call("$", quote(List), nm)) # ugly safe hack
>   [1] "xii"
> 
> With List[["name"]] syntax you get
>   > List <- list(Eleven=11, Twelve="xii")
>   > List[["E"]]
>   NULL
>   > List[["E"]] <- List[["E"]] + 100
>   > str(List)
>   List of 3
>    $ Eleven: num 11
>    $ Twelve: chr "xii"
>    $ E     : num(0) 
>   > List[["Eleven"]] <- List[["Eleven"]] + 100
>   > str(List)
>   List of 3
>    $ Eleven: num 111
>    $ Twelve: chr "xii"
>    $ E     : num(0) 
>   > nm <- "Twelve"
>   > List[[nm]]
>   [1] "xii"
> 
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
> 
> 
> > -----Original Message-----
> > From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> > Of Andrew Robinson
> > Sent: Thursday, February 07, 2013 12:52 PM
> > To: David Winsemius
> > Cc: r-help
> > Subject: Re: [R] why "object 'x' not found"?
> > 
> > Hi David,
> > 
> > The following is an interesting observation ...
> > 
> > On Friday, February 8, 2013, David Winsemius wrote:
> > 
> > >
> > > On Feb 7, 2013, at 10:20 AM, Winfried Moser wrote:
> > > ....
> > >
> > Notice that the '[[' function is superior in every way to the '$' function.
> > >
> > 
> > I'm curious to know whether you can point to some consolidated comparison?
> > 
> > Best wishes,
> > 
> > Andrew
> > 
> > 
> > --
> > Andrew Robinson
> > Director (A/g), ACERA
> > Department of Mathematics and Statistics            Tel: +61-3-8344-6410
> > University of Melbourne, VIC 3010 Australia               (prefer email)
> > http://www.ms.unimelb.edu.au/~andrewpr              Fax: +61-3-8344-4599
> > http://www.acera.unimelb.edu.au/
> > 
> > FAwR: http://www.ms.unimelb.edu.au/~andrewpr/FAwR/
> > SPuR: http://www.ms.unimelb.edu.au/spuRs/
> > 
> > 	[[alternative HTML version deleted]]
> > 
> > ______________________________________________
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-- 
Andrew Robinson  
Director (A/g), ACERA 
Department of Mathematics and Statistics            Tel: +61-3-8344-6410
University of Melbourne, VIC 3010 Australia               (prefer email)
http://www.ms.unimelb.edu.au/~andrewpr              Fax: +61-3-8344-4599
http://www.acera.unimelb.edu.au/

Forest Analytics with R (Springer, 2011) 
http://www.ms.unimelb.edu.au/FAwR/
Introduction to Scientific Programming and Simulation using R (CRC, 2009): 
http://www.ms.unimelb.edu.au/spuRs/