[R] short-hand to avoid use of length() in subsetting vectors?

[Eric Rupley]

Hi--

I suspect this is a frequently considered (and possibly asked) question, but I haven't thus far found an answer: 

	For slicing a vector with x[…], is there a symbol for length(x)?

I'm seeking a short-hand for referring to the length of vector one is trying to index.

E.g., for a data.frame, say,

> test.frame <-data.frame(matrix(c(1:100),ncol=10,nrow=10,byrow=T))
> names(test.frame) <- names(islands)[1:10]

is there a short-hand for subsetting

> test.frame$Baffin[1:(length(test.frame$Baffin)-3)]
[1]  6 16 26 36 46 56 66
> 
> 

that would allow one to avoid the "(length(some.dataframe$variable)-offset)"?

I was thinking something paralleling the use of negative indices in […] might exist with seq(from,to), e.g. for the above

> test.frame$Baffin[seq(,7)]
[1]  6 16 26 36 46 56 66
> 

works.  But the fantasy

	test.frame$Baffin[seq(,-3)]

obviously doesn't…

Any suggestions will be gratefully appreciated…

As always, many thanks to the patient list members who helps on these simple questions...

Best,
Eric



--
 Eric Rupley
 University of Michigan, Museum of Anthropology
 1109 Geddes Ave, Rm. 4013
 Ann Arbor, MI 48109-1079
 
 erupley at umich.edu
 +1.734.276.8572