[R] The end of Matlab

[Gabor Grothendieck]

Use tail and head. See interspersed.

On Thu, Dec 11, 2008 at 9:45 PM, Mike Rowe <mwrowe at gmail.com> wrote:
> Greetings!
>
> I come to R by way of Matlab.  One feature in Matlab I miss is its
> "end" keyword.  When you put "end" inside an indexing expression, it
> is interpreted as the length of the variable along the dimension being
> indexed.  For example, if the same feature were implemented in R:
>
> my.vector[5:end]

tail(my.vector, -4)

>
> would be equivalent to:
>
> my.vector[5:length(my.vector)]
>
> or:
>
> this.matrix[3:end,end]

tail(tail(this.matrix, -2), 1)

>
> would be equivalent to:
>
> this.matrix[3:nrow(this.matrix),ncol(this.matrix)]   # or
> this.matrix[3:dim(this.matrix)[1],dim(this.matrix)[2]]
>
> As you can see, the R version requires more typing, and I am a lousy
> typist.
>
> With this in mind, I wanted to try to implement something like this in
> R.  It seems like that in order to be able to do this, I would have to
> be able to access the parse tree of the expression currently being
> evaluated by the interpreter from within my End function-- is this
> possible?  Since the "[" and "[[" operators are primitive I can't see
> their arguments via the call stack functions...
>
> Anyone got a workaround?  Would anybody else like to see this feature
> added to R?
>
> Thanks,
> Mike
>
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