[R] Coalesce function in BBmisc, emoa, and microbenchmark packages

[Brian Diggs]

On 3/17/2012 6:24 AM, Paul Miller wrote:
> Hello All,
>
> Need to coalesce some columns using R. Looked online to see how this
> is done. One approach appears to be to use ifelse. Also uncovered a
> coalesce function in the BBmisc, emoa, and microbenchmark packages.
>
> Trouble is I can't seem to get it to work in any of these packages.
> Or perhaps I misunderstand what it's intended to do. The
> documentation is generally pretty scant.
>
> Working with two columns: Date of Death (DOD) and Last Known Date
> Alive (LKDA). One or the other column is populated for each of the
> patients in my dataframe and the other column is blank.
>
> When I run code like "with(Demographics, coalesce(DOD, LKDA))", the
> function generates a value whenever DOD is not missing and generates
> NA otherwise (even though the value for LKDA is not missing). So, for
> example, I get an NA for the 8th element below, even though I have a
> value of "2008-03-25" for LKDA.
>
>> with(Demographics, coalesce(DOD, LKDA))
> [1] "2006-07-23" "2008-07-09" "2007-12-16" "2008-01-19" "2009-05-05"
> "2006-04-29" "2006-06-18" NA
>
> At least that's what happens in the BBmisc and emoa packages. The
> microbenchmark package appears not to have a coalesce function though
> the documentation says it does. I think I've seen instances where a
> function gets removed from a package. So maybe that's what happened
> here.
>
> Thought maybe there is a difference between blank and NA as far as R
> or the function is concerned. The is.na() function seems to indicate
> that a blank is an NA. I also tried making the blanks into NA but
> that didn't help.
>
> Does anyone have experience with the coalesce function in any of the
> three packages? If so, can they help me understand what I might be
> doing wrong?

I didn't know about these other coalesce functions, but I had written my
own. Looking at them, they don't seem to be vectorized; mine is. That's
not to say that there may not be other problems with it.

##' Return first non-NA, vectorized
##'
##'
##' @param ... Vectors, all of the same length.
##' @return Vector of the same length as the input vectors, each
##' element of which is the first corresponding non-NA element in the
##' given vectors in the order they are specified
##' @author Brian Diggs
coalesce <- function(...) {
     dots <- list(...)
     ret <- Reduce(function (x,y) ifelse(!is.na(x),x,y), dots)
     class(ret) <- class(dots[[1]])
     ret
}

And using your example data:

Demographics <- data.frame(DOD = as.Date(c("2006-07-23", "2008-07-09",
                            "2007-12-16", "2008-01-19", "2009-05-05",
                            "2006-04-29", "2006-06-18", NA)),
                            LKDA = as.Date(c(NA, NA, NA, NA, NA, NA,
                            NA, "2008-03-25")))

 > with(Demographics, coalesce(DOD, LKDA))
[1] "2006-07-23" "2008-07-09" "2007-12-16" "2008-01-19" "2009-05-05"
[6] "2006-04-29" "2006-06-18" "2008-03-25"


> Thanks,
>
> Paul
>


-- 
Brian S. Diggs, PhD
Senior Research Associate, Department of Surgery
Oregon Health & Science University