[R] Question about creating lists with functions as elements

[Craig P. Pyrame]

Dear Henrique,

Thanks!  This does work, and I find the following solution to my 
original problem elegant enough:

 > rep(list(character, integer, numeric, ...), c(3, 2, 2, ...))

Best regards,
Craig



Henrique Dallazuanna wrote:
> From the help page of rep:
>
>
> "Value:
>
>      An object of the same type as 'x' (except that 'rep' will coerce
>      pairlists to vector lists)."
>
> So, you can do:
>
> rep(list(character), 2)
>
> On Tue, Jun 30, 2009 at 9:00 AM, Craig P. Pyrame <crappyr at gmail.com 
> <mailto:crappyr at gmail.com>> wrote:
>
>     Dear list,
>
>     I am trying to construct a list of functions using rep.  I can't
>     understand the following:
>
>     > c(character, character) => list with two functions
>     > rep(character, 2) => error
>
>     The error says that "object of type 'special' is not subsettable",
>     and I have no idea what this means.  Would you please help me.
>
>     The purpose of doing the above is that I need to use scan for
>     reading files that happen to be too large and a bit irregular for
>     read.table.  To make scan work, I need to specify the types of
>     values in each column (record field).  I can specify the 'what'
>     argument as follows:
>
>     > records <- scan(..., what = list(character(0), character(0),
>     integer(0), numeric(0), character(0), ...), ...)
>
>     but this quickly becomes boring for large enough records. (Why
>     does not scan take a character string with class names, as
>     read.table does, instead of a list with dummy objects?) So I am
>     trying to do tricks, and one idea that seems pretty simple is to
>     create a list of functions that create vectors of a particular
>     type, and apply them (using lapply) to get a list of prototype
>     objects:
>
>     > types = lapply(c(rep(character, 2), integer, numeric, ...),
>     function(type) type(0)) => error
>
>     But this fails, as above.  Why?  Why can c(character, character)
>     create a list of two functions, but rep(character, 2) can't?
>
>     Another solution to my problem I could find (and you'll hopefully
>     suggest an even better one) is to use class names instead, like so:
>
>     > types = lapply(c(rep('character', 2), 'integer', 'numeric',
>     ...), function(type) vector(type, 0))
>
>     but I am still curious why the above doesn't work as I would
>     expect it to.
>
>     Best regards,
>     Craig
>
>     ______________________________________________
>     R-help at r-project.org <mailto:R-help at r-project.org> mailing list
>     https://stat.ethz.ch/mailman/listinfo/r-help
>     PLEASE do read the posting guide
>     http://www.R-project.org/posting-guide.html
>     and provide commented, minimal, self-contained, reproducible code.
>
>
>
>
> -- 
> Henrique Dallazuanna
> Curitiba-Paraná-Brasil
> 25° 25' 40" S 49° 16' 22" O