[datatable-help] with=FALSE

[Steve Lianoglou]

Yeah -- I say we just leave it as is ...

On Tue, May 1, 2012 at 4:37 AM, Matthew Dowle <mdowle at mdowle.plus.com> wrote:
>
> Ok, makes sense. Unless anyone else chimes in, happy to leave it as it is
> then.
> Thanks, Matthew
>
>> Well, no one has chimed in yet, so I'll give it a shot.
>>
>> I see your logic, and I like your continual efforts to make the package
>> neater, but my take would be to leave things as they are for consistency.
>> I think it would be easier for new users to find that
>>     DT[,c("colA","colB")]
>> and
>>     colvars = c("colA","colB")
>>     DT[,colvars]
>> both don't work, and realize they need to use with=FALSE, rather than
>> finding that the two lead to different results.
>>
>> Joe Voelkel
>>
>>
>> -----Original Message-----
>> From: datatable-help-bounces at lists.r-forge.r-project.org
>> [mailto:datatable-help-bounces at lists.r-forge.r-project.org] On Behalf Of
>> Matthew Dowle
>> Sent: Thursday, April 26, 2012 5:03 AM
>> To: datatable-help at lists.r-forge.r-project.org
>> Subject: [datatable-help] with=FALSE
>>
>>
>> Dear Datatablers,
>>
>> It may be possible for these :
>>
>>     DT[,1]
>>     DT[,1:3]
>>     DT[,c("colA","colB")]
>>
>> all to return a data.table of those columns, rather than needing
>> with=FALSE, for convenience. After all, there is no useful purpose of
>> returning the j vector itself in these cases; the programmers intent is
>> unambiguous (afaik).
>>
>> Where a variable holds the vector of column names or numbers, with=FALSE
>> would still be needed.
>>
>>     colvars = c("colA","colB")
>>     DT[,colvars]  # would return the column called colvars if exists, or
>> the vector itself.
>>     DT[,colvars,with=FALSE]   # with needed in this case
>>
>> Given with=FALSE would become optional in the simpler cases, I'm thinking
>> it would be backwards compatible and wouldn't cause any problems to
>> existing code. Unless, there is a valid reason to return the j vector
>> straight back (a special case of a larger idiom perhaps)?
>>
>> Internally it would look at the j expression to see if it was a single
>> column position, a call to ":" or a call to "c()", which resulted in a
>> valid vector of column names or positions. Anything more complicated would
>> need with=FALSE.  The risk would be inconsistency and confusion, or not
>> maybe?
>>
>> This would change the very first FAQ (1.1), though. Not sure if it would
>> make it easier or harder to make the transition to data.table.
>>
>> Thoughts?
>>
>> Matthew
>>
>>
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>
>
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-- 
Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact