[R] The end of Matlab

[Gabor Grothendieck]

Its been pointed out to me that the second one is wrong.

It should be:

tail(this.matrix, -2)[, ncol(this.matrix)]

which is not as compact as matlab or my prior post but
still not particularly onerous.

On Thu, Dec 11, 2008 at 11:49 PM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> 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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>>
>