[R] Generic Functions and Dates

[Elliot Joel Bernstein]

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?


setGeneric("nan2last", function(x) { standardGeneric("nan2last") })                                                                                                                
                                                                                                                                                                                   
setMethod(nan2last, "vector",                                                                                                                                                      
          function(x) {                                                                                                                                                            
                                                                                                                                                                                   
            naLocs <- (1:length(x))[is.na(x)]                                                                                                                                      
                                                                                                                                                                                   
            if (length(naLocs) == 0)                                                                                                                                               
              return (x)                                                                                                                                                           
                                                                                                                                                                                   
            naLocs <- naLocs[naLocs>1]                                                                                                                                             
                                                                                                                                                                                   
            for (i in 1:length(naLocs)) {                                                                                                                                          
              x[naLocs[i]] <- x[naLocs[i]-1]                                                                                                                                       
            }                                                                                                                                                                      
                                                                                                                                                                                   
            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