R help - Jan 2012 - What does [[1]] mean?

I know that [] is used for indexing.
I know that [[]] is used for reference to a property of a COM object.

I cannot find any explanation of what [[1]] does or, more pertinently, where it
should be used.

Thank you.

	[[alternative HTML version deleted]]

Have you read ?"[[" ?

The short answer is that you can use both [] and [[]] on lists, the [] construct
will return a subset of  the list (which will be a list) while [[]] will return
a single element of the list (which could be a list or a vector or whatever that
element may be):  compare:
> tmp <- list( a=1, b=letters )
> tmp[1]
$a
[1] 1
> tmp[1] + 1
Error in tmp[1] + 1 : non-numeric argument to binary
operator
> tmp[[1]]
[1] 1
> tmp[[1]] + 1
[1] 2

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Ajay Askoolum
> Sent: Thursday, January 26, 2012 11:27 AM
> To: R General Forum
> Subject: [R] What does [[1]] mean?
> 
> I know that [] is used for indexing.
> I know that [[]] is used for reference to a property of a COM object.
> 
> I cannot find any explanation of what [[1]] does or, more pertinently,
> where it should be used.
> 
> Thank you.
> 
> 	[[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.

Here is a page that should help:

http://www.burns-stat.com/pages/Tutor/more_R_subscript.html

Also Circle 8.1.54 of 'The R Inferno'
http://www.burns-stat.com/pages/Tutor/R_inferno.pdf


On 26/01/2012 18:27, Ajay Askoolum wrote:
> I know that [] is used for indexing.
> I know that [[]] is used for reference to a property of a COM object.
>
> I cannot find any explanation of what [[1]] does or, more pertinently,
where it should be used.
>
> Thank you.
>
> 	[[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.
>
-- 
Patrick Burns
pburns at pburns.seanet.com
twitter: @portfolioprobe
http://www.portfolioprobe.com/blog
http://www.burns-stat.com
(home of 'Some hints for the R beginner'
and 'The R Inferno')