[R] index

Prof Brian Ripley ripley at stats.ox.ac.uk
Wed Jan 2 17:02:33 CET 2008

Is exp3 <- c(rep(NA, 3), seq_along(x)) what you are looking for?

> x[exp3][10]
[1] "g"

(I presume you meant x <- letters[1:10]: R is case-sensitive and you don't 
need c() to concatenate a single vector.)

On Wed, 2 Jan 2008, Antonio Gasparrini wrote:

> Dear all,
> I would like to know if it's possible to create an index for a 
> variable/vector that specifies the value in the n position before the 
> actual value.
> For example, if X <- c(letters[1:10]), x[10] is 'j'. I would like to 
> create an index exp3 (the third position before) such as if z <- 
> x[exp3], then z[10] = 'g'.
> In Stata that index is x[-3], but not in R.
> I have to input it in a very complex function to be minimised with the 
> mle command, so I can't solve this problem with a loop.
> Can you help me?

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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