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

[Harish]

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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