Dear all,
I sometimes use the following function:
Curry <- function(FUN,...) {
# by Byron Ellis,
https://stat.ethz.ch/pipermail/r-devel/2007-November/047318.html
.orig <- list(...)
function(...) do.call(FUN,c(.orig,list(...)))
}
... and have thought it might be convenient to have a method for [ doing
this. As a simple example,
> apply(M, 1, mean[trim=0.1]) # hypothetical equivalent to apply(M, 1,
Curry(mean, trim=0.1))
would be easier to understand than passing arguments by ...
> apply(M, 1, mean, trim=0.1)
and much shorter than using an anonymous function
> apply(M, 1, function(x) mean(x, trim=0.1)
This would be much more useful for complicated functions that may take
several functions as arguments. For example (my real examples are too long
but this seems general enough),
foo <- function(x, ...) {
dots <- list(...)
mapply(function(f) f(x), dots)
}
foo(1:10, mean, sd)
foo(c(1:10, NA), mean, mean[trim=0.1, na.rm=TRUE], sd[na.rm=TRUE])
Defining `[.function` <- Curry won't help:
> mean[trim=0.1]
Error in mean[trim = 0.1] : object of type 'closure' is not subsettable
One can write summary and other methods for class "function" without such
problems, so this has something to do with [ being a primitive function and
not using UseMethod, it would be foolish to re-define it as an "ordinary"
generic function.
Redefining mean as structure(mean, class="function") will make it work but
then one would have to do it for all functions which is not feasible.
> class(mean) <- class(mean)
> class(sd)<-class(sd)
> foo(c(1:10, NA), mean, mean[na.rm=TRUE], mean[trim=0.1, na.rm=TRUE],
sd[na.rm=TRUE])
[1] NA 5.500000 5.500000 3.027650
Or one could define a short-named function (say, .) doing this:
> rm(mean, sd) ## removing the modified copies from global environment
> .<-function(x) structure(x, class=class(x))
> foo(c(1:10, NA), mean, .(mean)[na.rm=TRUE], .(mean)[trim=0.1, na.rm=TRUE],
.(sd)[na.rm=TRUE])
But this is not as nice. (And neither is replacing "[" with "Curry" by using
substitute et al. inside `foo`, - this would make it usable only within
functions that one could be bothered to redefine this way - probably none.)
Thanks in advance for any ideas and comments (including the ones saying that
this is an awful idea)
Best regards,
Kenn
Kenn Konstabel
Department of Chronic Diseases
National Institute for Health Development
Hiiu 42
Tallinn, Estonia
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