Gavin,
I ran into the same cryptic "invalid subscript type 'closure'" message in
a slightly less complicated scenario, and wanted to post the cause in
my case (the root cause is probably the same either way).
Similarly to your case, I was subsetting a data frame. I had a list
of variable names corresponding to columns in the frame.
Unfortunately the variable name I had assigned to this list, var,
coincided with the name of a base package function in R for variance.
When I attempted to subset df[, var], I got the 'closure' error message,
but if I renamed the list of variable names so the collision didn't occur,
e.g. df[, vars] instead of df[, var], it worked as expected.
Sincerely,
Greg B. Hill
Gavin Simpson wrote:
>
> Dear List,
>
> I am writing a formula method for a function in a package I maintain. I
> want the method to return a data.frame that potentially only contains
> some of the variables in 'data', as specified by the formula.
>
> The problem I am having is in writing the function and wrapping it
> around model.frame. Consider the following data frame:
>
> dat <- data.frame(A = runif(10), B = runif(10), C = runif(10))
>
> And the wrapper function:
>
> foo <- function(formula, data = NULL, ..., subset = NULL,
> na.action = na.pass) {
> mt <- terms(formula, data = data, simplify = TRUE)
> mf <- model.frame(formula(mt), data = data, subset = subset,
> na.action = na.action)
> ## real function would do more stuff here and pass mf on to
> ## other functions
> mf
> }
>
> This is how I envisage the function being called. The real world use
> would have a data.frame with tens or hundreds of components where only a
> few need to be excluded. Hence wanting formulas of the form below to
> work.
>
> foo(~ . - B, data = dat)
>
> The aim is to return only columns A and C in an object returned by
> model.frame. However, when I run the above, I get the following error:
>
>> foo(~ A + B, data = dat)
> Error in xj[i] : invalid subscript type 'closure'
>
> I've tracked this down to the line in model.frame.default
>
> subset <- eval(substitute(subset), data, env)
>
> After evaluating this line, subset contains:
>
> Browse[1]> subset
> function (x, ...)
> UseMethod("subset")
> <environment: namespace:base>
>
> Not NULL, and hence the error later on when calling the internal
> model.frame code.
>
> So the question is, what am I doing wrong?
>
> If I leave the subset argument out of the definition of foo and rely
> upon the default in model.frame.default, the function works as
> expected.
>
> Perhaps the question should be, how do I modify foo() to allow it to
> have a formal subset argument, passed to model.frame?
>
> Any other suggestions gratefully accepted.
>
> Thanks in advance,
>
> G
> --
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> Dr. Gavin Simpson [t] +44 (0)20 7679 0522
> ECRC, UCL Geography, [f] +44 (0)20 7679 0565
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