On 01/31/2011 12:15 PM, Elliot Joel Bernstein wrote:
> I'm trying to write a generic function that calls different methods
> depending on the structure of the argument, but not the exact type of
> its contents. For example, the function 'nan2last' below works for a
> numeric vector but not for a vector of Date objects. Is there any way
> to make it work on any vector?
Hi Elliot --
In principle one could write a method that advertises that it operates
on signature "ANY"
setMethod(nan2last, "ANY", function(x) <...>)
but in practice it's unlikely that one could do something useful on
_any_ object.
If I
> getClass("Date")
Virtual Class "Date" [package "methods"]
Slots:
Name: .S3Class
Class: character
Extends: "oldClass"
I see that Date does not extend "vector", so I'd write a method that
delegates as appropriate, along the lines of
.nan2last <- function(x) { <general implementation> }
setMethod(foo, "vector", .na2last)
setMethod(foo, "Date", .na2last)
> setGeneric("nan2last", function(x) { standardGeneric("nan2last") })
>
> setMethod(nan2last, "vector",
> function(x) {
>
> naLocs <- (1:length(x))[is.na(x)]
probably naLocs <- which(is.na(x))
>
> if (length(naLocs) == 0)
> return (x)
>
> naLocs <- naLocs[naLocs>1]
>
> for (i in 1:length(naLocs)) {
seq_along(naLocs), otherwise you'll surprise yourself with
1:length(integer(0))
> x[naLocs[i]] <- x[naLocs[i]-1]
> }
just x[naLocs] <- x[naLocs - 1], outside the loop (so no seq_along)
Martin
>
> return(x)
> })
>
> ## Works
> x <- 1:10;
> x[sample(10,3)] <- NA
> print(cbind(x, nan2last(x)))
>
> ## Doesn't work
> x <- seq(as.Date("2011-01-01"), as.Date("2011-01-31"), "days")
> x[sample(length(x), 5)] <- NA
> nan2last(x)
>
> Thanks.
>
> - Elliot
>
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