[datatable-help] data.table inherits from data.frame [was:Auto-convert characters to factors when settings keys?]

Harish harishv_99 at yahoo.com
Wed Jun 30 01:31:19 CEST 2010 

Option ii -- creating a wrapper around the data.frame creation function -- does not work with melt() when I tested it.  When I glanced through the code, I did not see any calls to data.frame().  It looks like it uses rbind() and cbind() to create the new data.frame.

Option i -- I'm not sure what this entails.  What is the advantage over having wrapper functions?  Reshape-type functions interest me at the moment.


Harish


--- On Mon, 6/28/10, mdowle at mdowle.plus.com <mdowle at mdowle.plus.com> wrote:

> From: mdowle at mdowle.plus.com <mdowle at mdowle.plus.com>
> Subject: Re: [datatable-help] data.table inherits from data.frame  [was:Auto-convert characters to factors when settings keys?]
> To: "Short, Tom" <TShort at epri.com>
> Cc: "Harish" <harishv_99 at yahoo.com>, datatable-help at lists.r-forge.r-project.org
> Date: Monday, June 28, 2010, 10:33 AM
> Yes if the function uses data.frame()
> to create the object it returns,
> then it should return a data.frame e.g. melt
> (untested).  If it just calls
> "[", or similar, on the object then it should keep it as
> data.table e.g.
> subset (tested).  The main thing is they work though,
> so that other
> packages using those functions also work e.g. ggplot.
> 
> For returning results back to a data.table aware
> environment though ...
> 
> i) We could add data.table methods for melt, reshape, etc.
> These could
> either use the data.table equivalent syntax and efficiency,
> easing users
> into it (think someone mentioned that before), or these
> methods could call
> the package's function returning a data.frame, and then
> make the class
> change before returning data.table.  Is it just/mainly
> reshape people
> would want data.table methods for?
> 
> ii) Or, possibly, try this in .GlobalEnv :
> 
>    data.frame = function(...)
> as.data.table(base::data.frame(...))
> 
> and those functions, such as melt, may well then return
> data.table
> (untested).  IF that works, then it could be made more
> flexible :
> 
>    data.frame = function(...) {
>       if (cendta())
> as.data.table(base::data.frame(...))
>       else base::data.frame(...)
>    }
> 
> so users such as you or I, know we really do want a true
> data.frame, but
> non-data-data-aware environments would really create
> data.table for us
> (while still using [.data.frame on them). We would need to
> export cendta
> if users were to do that, in the meantime try
> data.table:::cendta().
> 
> Anyway ... way further than I expected to go. If anyone
> feels like testing
> that, would be interested if it works! Thanks for the
> interest and
> question.
> 
> Matthew
> 
> 
> > Harish, you'll still (usually) get back a data.frame
> in that situation.
> > There may be a situation involving just manipulation
> of the original where
> > the function keeps the object as a data.table.
> Auto-converting return
> > values would be a challenge.
> >
> > - Tom
> >
> >
> >
> >
> >> -----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 Harish
> >> Sent: Monday, June 28, 2010 11:57
> >> To: datatable-help at lists.r-forge.r-project.org
> >> Subject: Re: [datatable-help] data.table inherits
> from
> >> data.frame [was:Auto-convert characters to factors
> when
> >> settings keys?]
> >>
> >> Removing the requirement for explicit conversions
> simplifies
> >> things a bit.  Thanks.
> >>
> >> You commented on arguments passed into a
> function.  What
> >> happens to return values?  For example, the
> reshape functions
> >> (reshape(), cast(), melt(), etc.) returns a
> data.frame.  Are
> >> those automatically treated to be data.table in
> the workspace
> >> that is data.table aware?
> >>
> >>
> >> Harish
> >>
> >>
> >> --- On Mon, 6/28/10, mdowle at mdowle.plus.com
> >> <mdowle at mdowle.plus.com>
> wrote:
> >>
> >> > From: mdowle at mdowle.plus.com
> <mdowle at mdowle.plus.com>
> >> > Subject: [datatable-help] data.table inherits
> from data.frame [was:
> >> > Auto-convert characters to factors when
> settings keys?]
> >> > To: mailinglist.honeypot at gmail.com
> >> > Cc: datatable-help at lists.r-forge.r-project.org
> >> > Date: Monday, June 28, 2010, 3:03 AM
> >> >
> >> > The subject of this thread got misleading
> too. Changing that now.
> >> > Was: Auto-convert characters to factors when
> settings keys?
> >> >
> >> >
> >> > Thanks Steve,
> >> >
> >> > There are two types of users of data.table.
> Ones who know they are
> >> > using it, and ones that don't. This change is
> for the latter. If a
> >> > base function that only accepts data.frame,
> such as subset for
> >> > example, does dt[,c('b','c')] inside it, then
> that actually
> >> does work
> >> > and returns the columns, not c('b','c').
> >> >
> >> > For example, at the end of subset.data.frame
> there is :
> >> >
> >> >     x[r, vars, drop = drop]
> >> >
> >> > and that will use [.data.frame even though x
> is data.table. 
> >>  subset is
> >> > a base function and as such isn't a
> data.table aware user.
> >> >
> >> > However, when a user (such as you or I) uses
> data.table,
> >> then we can
> >> > use its features such as i and j expressions
> of column names, joins
> >> > using x[y][z] syntax, etc.  No changes
> there.  If we want
> >> > dt[,c("b","c")] to return the columns, then
> we will still have to
> >> > convert to data.frame, as before.  Thats
> because we work in
> >> our user
> >> > workspace which is data.table aware.
> >> >
> >> > It depends on where [.data.table was called
> from.
> >> >
> >> > Its just so that packages (e.g. ggplot), and
> base
> >> functions, can work
> >> > with data.table more easily now, without
> removing any of the
> >> > advantages of the [.data.table syntax, and
> without requiring
> >> > conversion.
> >> >
> >> > Makes more sense now hopefully ?
> >> >
> >> > Matthew
> >> >
> >> >
> >> > > Hi,
> >> > >
> >> > > On Sun, Jun 27, 2010 at 6:47 PM, Matthew
> Dowle
> >> > > <mdowle at mdowle.plus.com>
> >> > > wrote:
> >> > >> I went back to try again with S3
> inheritance,
> >> > discussed further up in
> >> > >> this thread.  Just committed as it
> seems, so far,
> >> > to work.
> >> > >>
> >> > >> * data.table now inherits from
> data.frame i.e.
> >> > class =
> >> > >> c("data.table","data.frame")
> >> > >> * is.data.frame() now returns TRUE
> for data.table
> >> > >> * data.table should now be
> compatible with
> >> > functions and packages that
> >> > >> _only_ accept data.frame.
> >> > >
> >> > > Perhaps I lost the point of this
> conversation
> >> > somewhere along the way,
> >> > > but this change makes it *technically*
> compatible
> >> > since a data.table
> >> > > passes an is.data.frame test, but it
> doesn't work in
> >> > ways that are
> >> > > perfectly acceptable for some function
> accepting a
> >> > data.frame to work,
> >> > > ie:
> >> > >
> >> > > R> library(data.table)
> >> > > R> dt <- data.table(a=1:5,
> b=letters[1:5],
> >> > c=sample(1:100, 5))
> >> > > R> dt[,c('b', 'c')]
> >> > > [1] "b" "c"
> >> > >
> >> > > instead of
> >> > >
> >> > > R> df <- as.data.frame(dt)
> >> > > R> df[,c('b', 'c')]
> >> > >   b  c
> >> > > 1 a 18
> >> > > 2 b 11
> >> > > 3 c  2
> >> > > 4 d 50
> >> > > 5 e 96
> >> > >
> >> > > Unless you were talking about making
> more changes to
> >> > make a data.table
> >> > > act more like a data.frame, I'm not sure
> allowing the
> >> > user to ignore
> >> > > the differences between
> data.table/frames is really a
> >> > win/win
> >> > > situation.
> >> > >
> >> > > Sorry if I missed something.
> >> > > -steve
> >> > >
> >> > > --
> >> > > 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
> >> > >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
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> >> >
> >> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable
> >> > -help
> >> >
> >>
> >>
> >>
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> 
>

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