[R] apply problem

[ripley@stats.ox.ac.uk]

On Sun, 17 Mar 2002 ggrothendieck at yifan.net wrote:

>
> > > > apply(iris3,1,function(x)identical(x,iris3[1,]))
> > >     1     2     3
> > > FALSE FALSE FALSE
> > >
> > > What's wrong here?
> >
> > iris3 is not an array, so it it coerced to one via as.matrix
> [...]
> > and that's not the same object as your iris3
>
> Thanks.
>
> Is there a way to iterate over the rows of a data
> frame without writing a loop -- that was my
> original objective.

No.  A row of a data frame is still a data frame and therefore arbitrarily
complex.

In any case, in R apply() does write a loop.  There are lots of legacy
myths about the efficiencies of loops vs *apply(), but the reality it
depends on the exact version of your S engine (and perhaps on how much
memory you have).

Just for the record, lapply() is the way to iterate over columns of a data
frame.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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