[R] update search path for attached data

[Ulrich Leopold]

On Fri, 2008-07-04 at 15:13 +0100, Prof Brian Ripley wrote:
> On Fri, 4 Jul 2008, Ulrich Leopold wrote:
>
> > Dear list,
> >
> > is there a way of updating the search path when using attach() for a data
set.
> >
> > I am overwriting a variable in a data frame. To update teh search path I do
> > the follwoing:
> >
> >> attach(dataset)
> >> some data manipulation of dataset
> >> detach(dataset)
> >> attach(dataset) # to update the search path
> >
> > Is there a way to avoid the numerous detach() and attach() commands?
>
> Not if 'dataset' is that data frame (you didn't actually say).  From the
> help page:
>
>       The database is not actually attached.  Rather, a new environment
>       is created on the search path and the elements of a list
>       (including columns of a data frame) or objects in a save file or
>       an environment are _copied_ into the new environment.  If you use
>       '<<-' or 'assign' to assign to an attached database, you only
>       alter the attached copy, not the original object.
>
> So you can both change the data frame and assign the column to pos=2 to
> get the effect of what you appear to want.

How can I update directly the search path without using detach()
attach() or '<<-' assign()?
Maybe using attach() or assign methods is not so convenient anyway in my
case as it creates always a copy of each data set?

Is there a good practise in programming in R by using search paths but
keep memory as well as updating of the search path to a minimum?

Ulrich

-- 
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Ulrich Leopold

Resource Centre for Environmental Technologies, Public Research Centre
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Computational Bio- and Physical Geography, Institute for Biodiversity
and Ecosystem Dynamics, University of Amsterdam, Nieuwe Achtergracht
166, NL-1018WV Amsterdam, The Netherlands

http://www.science.uva.nl/ibed