[R] confusion with R syntax

[Andrew Robinson]

Hi Mark,

what's happening here is that R is applying the one-dimensional
subscripting operations sequentially.

Try

x <- seq(1,10)
x[2:4][1]

Cheers

Andrew

On Thu, Oct 11, 2007 at 03:34:22PM -0400, Leeds, Mark (IED) wrote:
> I just noticed something by accident with R syntax that I'm sure is
> correct but I don't understand it. If I have
> a simple numeric vector x and I subscript it, it seems that I can then
> subscript a second time with TRUE
> or FALSE, sort of like a 2 dimensional array in C. Does someone know if
> this is documented somewhere
> Because it's neat but I never knew it existed. To me it seems like a 1
> dimensional vector should
> have only one dimensional indexing ?
> 
> x <- seq(1,10)
> > x
>  [1]  1  2  3  4  5  6  7  8  9 10
> > x[2:4][c(TRUE,FALSE,TRUE)]
> [1] 2 4
> 
> But, it only works for TRUE or FALSE and not numbers so I think it's not
> really 2 dimensional indexing.
> 
> x[1][2]
> 
> [1] NA
> 
> If someone could explain this mechanism or tell me what I should look
> for in the archives, it would
> be appreciated. Thanks.
> --------------------------------------------------------
> 
> This is not an offer (or solicitation of an offer) to bu...{{dropped:22}}
> 
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-- 
Andrew Robinson  
Department of Mathematics and Statistics            Tel: +61-3-8344-9763
University of Melbourne, VIC 3010 Australia         Fax: +61-3-8344-4599
http://www.ms.unimelb.edu.au/~andrewpr
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