R help - Jan 2012 - using "list=" to force evaluation before execution

Dear all,

I have noticed that the expression 'list =' is sometimes used to tell R
to
evaluate something before executing it.

Two examples:

rm(list=ls())

a = 3
myVarName = 'a'
save(list=myVarName, file=...)


I was wondering whether there is any documentation on this way of using
"list". Which is a clearly different use than what ?list talks about,
as
the latter addresses the use of 'list' as a datastructure.

Thanks for your help,

Adi

	[[alternative HTML version deleted]]

Read the documentation for those two commands and you will see that
'list' is just a parameter to the function.  It would have been called
'xyz' and worked the same.  The is nothing special about 'list
=' in
this context; it is just naming a parameter to the function.

On Thu, Jan 12, 2012 at 11:55 AM, Aditya Bhagwat
<bhagwataditya at gmail.com> wrote:
> Dear all,
>
> I have noticed that the expression 'list =' is sometimes used to
tell R to
> evaluate something before executing it.
>
> Two examples:
>
> rm(list=ls())
>
> a = 3
> myVarName = 'a'
> save(list=myVarName, file=...)
>
>
> I was wondering whether there is any documentation on this way of using
> "list". Which is a clearly different use than what ?list talks
about, as
> the latter addresses the use of 'list' as a datastructure.
>
> Thanks for your help,
>
> Adi
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.


-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

Nope - you misunderstand entirely. Both of those functions have an argument
named "list" and the code you quote is just the standard way of using
a named argument. It could just as well read

rm(salmon = ls())

but that would be absurd. The list argument gets its name from the fact it
(usually) takes a list**, no more no less.

Michael

**Not strictly true here as ls() doesn't return a list, but just go with it.
It's a vector of names, not a list in the data structure sense.

On Jan 12, 2012, at 11:55 AM, Aditya Bhagwat <bhagwataditya at gmail.com>
wrote:
> Dear all,
> 
> I have noticed that the expression 'list =' is sometimes used to
tell R to
> evaluate something before executing it.
> 
> Two examples:
> 
> rm(list=ls())
> 
> a = 3
> myVarName = 'a'
> save(list=myVarName, file=...)
> 
> 
> I was wondering whether there is any documentation on this way of using
> "list". Which is a clearly different use than what ?list talks
about, as
> the latter addresses the use of 'list' as a datastructure.
> 
> Thanks for your help,
> 
> Adi
> 
>    [[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.