[R] programming questions

[ivo welch]

thanks, eric---I need a little more clarification.  *yes, I write
functions and then forget them.  so I want them to be self-sufficient.
 I want to write functions that check all their arguments for
validity.)  For example,

  my.fn <- function( mylist ) {
      stop.if.not( is.defined(mylist) )  ## ok, superfluous
      stop.if.not( is.defined(mylist$dataframe.in.mylist ))
      stop.if.not( is.defined(mylist$dataframe.in.mylist$a.component.I.need) )
      ### other checks, such as whether the component I need is long
enough, positive, etc.
      ### could be various other operations
      mylist$dataframe.in.mylist$a.component.I.need
  }

so

  my.fn( asd )   ## R gives me an error, asd is not in existence
  my.fn( NULL )  ## second error: the list component
'dataframe.in.mylist' I need is not there
  my.fn( data.frame( some.other.component=1:4 ) )  ## second error;
the list component  'dataframe.in.mylist' I need is not there
  my.fn( list( hello=1, silly=data.frame( x=1:4 ) ) ) ## second error:
dataframe.in.mylist does not exist
  my.fn( list( hello=2, dataframe.in.mylist= data.frame(
a.component.I.need=1:4 ))  ## ok

exists() works on a "stringified" variable name.  how do I stringify in R?


PS: btw, is it possible to weave documentation into my user function,
so that I can type "?is.defined" and I get a doc page that I have
written?  Ala perl pod.  I think I asked this before, and the answer
was no.

/iaw



----
Ivo Welch (ivo.welch at brown.edu, ivo.welch at gmail.com)
CV Starr Professor of Economics (Finance), Brown University
http://www.ivo-welch.info/





On Wed, Nov 3, 2010 at 3:40 PM, Erik Iverson <eriki at ccbr.umn.edu> wrote:
>
>> alas, should R not come with an is.defined() function?
>
> ?exists
>
> a variable may
>>
>> never have been created, and this is different from a variable
>> existing but holding a NULL.  this can be the case in the global
>> environment or in a data frame.
>>
>>  > is.null(never.before.seen)
>>  Error: objected 'never.before.seen' not found
>>  > is.defined(never.before.seen)  ## I need this, because I do not
>> want an error:
>>  [1] FALSE
>
> exists("never.before.seen") #notice the quotes
> [1] FALSE
>
>>
>> your acs function doesn't really do what I want, either, because {
>> d=data.frame( x=1:4); exists(acs(d$x)) } tells me FALSE .  I really
>> need
>>
>>  > d <- data.frame( x=1:5, y=1:5 )
>>  > is.defined(d$x)
>>  TRUE
>
> with(d, exists("x"))
>
>>  > is.defined(d$z)
>>  FALSE
>
> with(d, exists("z"))
>
>>  > is.defined(never.before.seen)
>>  FALSE
>
> exists("never.before.seen")
>
>>  > is.defined(never.before.seen$anything)  ## if a list does not
>> exist, anything in it does not exist either
>>  FALSE
>
> This one I'm a bit confused about.  If you're
> programming a function, then the user either:
>
> 1) passes in an object, which is bound to a
> local variable, and therefore exists. You can
> do checks on that object to see that it conforms
> to any constraints you have set.
>
> 2) does not pass in the object, in which case
> you can test for that with ?missing.
>
> Is writing your own functions for others to
> use what you're doing?
>
> --Erik
>
>