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

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)"?

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Steve Lianoglou
Sent: Tuesday, January 10, 2012 3:28 PM
To: Eric Rupley
Cc: r-help at r-project.org
Subject: Re: [R] short-hand to avoid use of length() in subsetting
vectors?

Hi,

On Tue, Jan 10, 2012 at 6:04 PM, Eric Rupley <erupley at umich.edu> wrote:

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)"?

Sadly there is no shorthand of the (exact) type you are looking for.

You can access the data like so, however:

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

I think that's as good as you're going to get, but let's see what
other suggestions pop up.

-steve

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