[Rd] error in install.packages() (PR#14042)

[William Dunlap]

> -----Original Message-----
> From: r-devel-bounces at r-project.org 
> [mailto:r-devel-bounces at r-project.org] On Behalf Of Duncan Murdoch
> Sent: Wednesday, November 04, 2009 8:47 AM
> To: michael.m.spiegel at gmail.com
> Cc: R-bugs at r-project.org; r-devel at stat.math.ethz.ch
> Subject: Re: [Rd] error in install.packages() (PR#14042)
> 
> On 11/4/2009 11:05 AM, michael.m.spiegel at gmail.com wrote:
> > Full_Name: Michael Spiegel
> > Version: 2.10
> > OS: Windows Vista
> > Submission from: (NULL) (76.104.24.156)
> > 
> > 
> > The following error is produced when attempting to call 
> install.packages.  Here
> > is the results of the traceback:
> > 
> >> source('http://openmx.psyc.virginia.edu/getOpenMx.R')
> > Error in f(res) : invalid subscript type 'list'
> >> traceback()
> > 7: f(res)
> > 6: available.packages(contriburl = contriburl, method = method)
> > 5: .install.winbinary(pkgs = pkgs, lib = lib, contriburl = 
> contriburl, 
> >        method = method, available = available, destdir = destdir, 
> >        dependencies = dependencies, ...)
> > 4: install.packages(pkgs = c("OpenMx"), repos = repos)
> > 3: eval.with.vis(expr, envir, enclos)
> > 2: eval.with.vis(ei, envir)
> > 1: source("http://openmx.psyc.virginia.edu/getOpenMx.R")
> > 
> > I've tracked the error down to somewhere in 
> available.packages defined in
> > src\library\utils\R\packages.R.  I am guessing that the 
> error in version 2.10
> > has something to do with the change: "available.packages() 
> gains a 'filters'
> > argument for specifying the filtering operations performed 
> on the packages found
> > in the repositories."
> 
> I've found the error, and will fix and commit to R-devel and 
> R-patched.
> 
> For future reference:  the problem was that it assigned the result of 
> sapply() to a subset of a vector.  Normally sapply() simplifies its 
> result to a vector, but in this case the result was empty, so 
> sapply() 
> returned an empty list; assigning a list to a vector coerced 
> the vector 
> to a list, and then the "invalid subscript type 'list'" came 
> soon after.

I've run into this sort of problem a lot (0-long input to sapply
causes it to return list()).  A related problem is that when sapply's
FUN doesn't always return the type of value you expect for some
corner case then sapply won't do the expected simplication.  If
sapply had an argument that gave the expected form of FUN's output
then sapply could (a) die if some call to FUN didn't return something
of that form and (b) return a 0-long object of the correct form
if sapply's X has length zero so FUN is never called.  E.g.,
   sapply(2:0, function(i)(11:20)[i], FUN.VALUE=integer(1)) # die on
third iteration
   sapply(integer(0), function(i)i>0, FUN.VALUE=logical(1)) # return
logical(0)

Another benefit of sapply knowing the type of FUN's return value is
that it wouldn't have to waste space creating a list of FUN's return
values but could stuff them directly into the final output structure.
A list of n scalar doubles is 4.5 times bigger than double(n) and the
factor is 9.0 for integers and logicals.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

> 
> Duncan Murdoch
> 
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