[R] Returning the name of an object passed directly or from a list by lapply

[Peter Ehlers]

On 2011-09-16 16:27, andrewH wrote:
> Dear Bill--
> Wow. This is very clever and I learned a lot from it. I've never seen the
> ...() trick before, and on a Google code search, I could not find anyone
> else who had used it. And I've never used the "..." feature, which, BTW,
> though mentioned in every intro to R text, has no help page I can find.
> <grrr>

Look for 'dot-dot-dot' in the 'R Language Definition' manual
(sec. 2.1.9).

Peter Ehlers

>
> Your function is still not doing what I am trying to do, doubtless because I
> was not clear enough in the question I pose  At the bottom of this message I
> have posted a copy of my testing function, and a few objects to test it on.
> Its details are unimportant and not very interesting, but note that all of
> its important outputs are in the form of side effects.   What I would like
> to be able to do is this:
>
> f(fun,<n variable names>)
> and get back this:
> fun(variable#1)
> fun(variable#2)
> ...
> fun(variable#n)
>
> Attempting to copy some of your techniques, I came up with this:
> evaluate<- function(fun, ...){
> unevaluatedArgs<- substitute(...)
> for (i in 1:length(deparse(unevaluatedArgs)))
> fun(deparse(unevaluatedArgs)[i])
> invisible(TRUE)
> }
> As applied to my test data, it works on the first variable (but gets the
> variable name wrong) and ignores the remainder of the list, e.g.:
>
>> evaluate(testX, H.char, H.vec, H.df,  H.mat)
> ###################
> testX( deparse(unevaluatedArgs)[i] ):  Class= character  Type= character
> Mode= character
> Summary:
>     Length     Class      Mode
>          1 character character
> Structure:
>   chr "H.char"
>
> On the other hand, this almost works:
> evaluate<- function(fun, ...){
> evaluatedArgs<- list(...)
> for (i in 1:length(evaluatedArgs))  fun(evaluatedArgs[i])
> invisible(TRUE)
> }
>
> The only thing it does not do is get the name of the passed object right.
> That seems like it ought to be a small problem, but as you pointed out, the
> names are not in the list.  (BTW, I don't understand dropping the names as a
> design choice for the list() function. If you use list() to make a list out
> of four symbols for objects, wouldn't it be better to make the text of the
> symbols the default names for those objects? That would solve this problem
> nicely.) [s]ubstitute seems to drop all but the first variable passed by
> "...".
>
> Thanks so much for your thoughtful help.
>
> andrewH
>
>
>
> testX<- function(objectX, bar=TRUE) {    # A useful diagnostic function
>      object.name<- deparse(substitute(objectX))
>      if(bar) cat("##################################\n");
>      cat("testX(", object.name, "): ");  cat(" Class=", class(objectX));
> cat("  Type=", typeof(objectX)); cat("  Mode=", mode(objectX), "\n");
>      cat("Summary:\n"); print(summary(objectX))
>      cat("Structure:\n");  str(objectX);
>      if (is.factor(objectX)) {cat("Levels: ", levels(objectX), "\n");
> cat("Length: ", length(objectX), "\n")}
>      invisible(object.name)
> }
>
> ## Define 4 test variables: H.char, H.vec, H.df, H.mat
> H.char<- letters[1:10]
> H.vec<- c(1:10)
> H.df<- {  # Makes a test data set A.df with 2-, 3-,&  4-factor sorting
> variables, making 24
> # combinations,&  a 4th variable with a  unique data value for each
> combination.
> # No random component.
>     year.2<- factor( rep(1:2, each=12) )
>     cohort.3<- factor( rep(rep(1:3,each=4),2) )
>     race.4<- factor( rep(1:4, 6) )
>     D1<- as.numeric(as.character(year.2))*1.1 +
> as.numeric(as.character(cohort.3))*1.01+
> as.numeric(as.character(race.4))*1.001
>     data.frame(year.2,cohort.3,race.4,D1)
> }
> H.mat<-matrix(1:16, 4, 4)
> ## End of test variables
>
> --
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>
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