On Wed, 13 Aug 2008, Tony Plate wrote:
Ben Bolker wrote:I'm looking for advice on manipulating parameters that are going to be passed through to another function. Specifically, I am working on my version of "mle", which is a wrapper for optim (among other optimizers). I would prefer not to replicate the entire argument list of optim(), so I'm using ... to pass extra arguments through. However: the starting values are specified as a list, which means that users can potentially specify them in any order (or at least that's the way it works now -- one solution to the problem I'm about to state is to insist that they specify the parameters in the same order as they are given in the arguments of the objective function). However, there are other arguments (lower, upper, control$parscale, control$ndeps) that should all be in the same order as the objective function definition by the time they get to optim()). I can think of a few solutions: (1) make the user specify them all in the right order (ugh) (2) add all of them as explicit parameters to my function so that I can rearrange them appropriately (ugh) (3) mess with the ... argument before it gets passed through to optim (impossible?) (4) capture ... as arglist <- list(...), manipulate the arguments as necessary, then pass them along to optim as do.call("optim",arglist) (ugh but maybe the best solution?) any thoughts?here's my two cents: - require names on parameters, rather than order
- construct calls and use eval() rather than do.call() (then you can manipulate list(...) without the ugh factor of do.call() -- though is do.call() any different to eval() in R? -- I know in S-PLUS that the use of do.call() can completely blow out memory usage)
do.call is just a way to construct and eval() calls. Since it is internal C code it does it quite efficiently.
- to avoid manually duplicating arg lists, use constructs like names(formals(optim)) and pmatch to find args that below to the optimizer function vs the objective function
Using wrappers is a better idea: you can see the idea in several places in the base graphics code.
-- Brian D. Ripley, [EMAIL PROTECTED] 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 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
