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[naLocs1]
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)))
