[Rd] data frame subset patch, take 2

Robert Gentleman rgentlem at fhcrc.org
Wed Dec 13 21:47:38 CET 2006

Robert Gentleman wrote:
> Hi,
>    We had the "names" discussion and, AFAIR, the idea that someone might 
> misinterpret the output as suggesting that one could index by number, 
> seemed to kill it. A more reasonable argument against is that names<- is 
> problematic.
> You can use $, [[ (with character subscripts), and yes ls does sort of 
> do what you want (but sorts the values, not sure if that is good). I 
> think it is also inefficient in that I believe it copies the CHARSXP's 
> (not sure we really need to do that, but I have not had time to sort out 

  I misremembered - it does not copy CHARSXPs.

> the issues). And there is an eapply as well, so ls() is not always needed.
> mget can be used to retrieve multiple values (and should be much more 
> efficient than multiple calls to get). There is no massign (no one seems 
> to have asked for it), and better design choice might be to vectorize 
> assign.
> best wishes
>    Robert
> Vladimir Dergachev wrote:
>> On Wednesday 13 December 2006 1:23 pm, Marcus G. Daniels wrote:
>>> Vladimir Dergachev wrote:
>>>>     2. It would be nice to have true hashed arrays in R (i.e. O(1) access
>>>> times). So far I have used named lists for this, but they are O(n):
>>> new.env(hash=TRUE) with get/assign/exists works ok.  But I suspect its
>>> just too easy to use named lists because it is easy, and that has bad
>>> performance ramifications for user code (perhaps the R developers are
>>> more vigilant about this for the R code itself).
>> Cool, thank you ! 
>> I wonder whether environments could be extended to allow names() to work 
>> (altough I see that ls() does the same function) and to allow for(i in E) 
>> loops.
>>                        thank you
>>                                Vladimir Dergachev
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Robert Gentleman, PhD
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M2-B876
PO Box 19024
Seattle, Washington 98109-1024
rgentlem at fhcrc.org

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