[R] zero index and lazy evaluation in ifelse()

[John Fox]

Dear Denis,

b[a] gives you c(1, 2, 3) (try it), which is recycled as c(1, 2, 3, 1); the
elements in positions 2, 3, and 4 of this vector (i.e., where a != 0) are 2,
3, 1.

Regards,
 John

--------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario
Canada L8S 4M4
905-525-9140x23604
http://socserv.mcmaster.ca/jfox 
-------------------------------- 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of 
> White.Denis at epamail.epa.gov
> Sent: Thursday, January 13, 2005 3:43 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] zero index and lazy evaluation in ifelse()
> 
> I don't understand this behavior:
> 
> > a <- c(0, 1, 2, 3)
> > b <- c(1, 2, 3, 4)
> > ifelse (a == 0, 0, b[a])
> [1] 0 2 3 1
> 
> rather than the desired 0 1 2 3.  Thanks for any explanation.
> 
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