[R] Sum function and missing values --- need to mimic SAS sum function

[Hervé Pagès]

Hi Martin,

On 01/26/2015 04:45 AM, Martin Maechler wrote:
>>>>>> Jim Lemon <drjimlemon at gmail.com>
>>>>>>      on Mon, 26 Jan 2015 11:21:03 +1100 writes:
>
>      > Hi Allen, How about this:
>
>      > sum_w_NA<-function(x) ifelse(all(is.na(x)),NA,sum(x,na.rm=TRUE))
>
> Excuse, Jim, but that's yet another  "horrible misuse of  ifelse()"
>
> John Fox's reply *did* contain  the "proper" solution
>
>       if (all(is.na(x))) NA else sum(x, na.rm=TRUE)
>
> The ifelse() function should never be used in such cases.
> Read more after googling
>
>      "Do NOT use ifelse()"
>
>      -- include the quotes in your search --
>
> or directly at
>     http://stat.ethz.ch/pipermail/r-help/2014-December/424367.html

Interesting. You could have added the following item to your list:

   4. less likely to play strange tricks on you:

      > ifelse(TRUE, a <- 2L, a <- 3L)
      [1] 2
      > a
      [1] 3

Yeah I've seen people using ifelse() that way and being totally
confused...

Cheers,
H.

>
> Yes, this has been on R-help a month ago..
> Martin
>
>      > On Mon, Jan 26, 2015 at 10:21 AM, Allen Bingham
>      > <aebingham2 at gmail.com> wrote:
>      >> I understand that in order to get the sum function to
>      >> ignore missing values I need to supply the argument
>      >> na.rm=TRUE. However, when summing numeric values in which
>      >> ALL components are "NA" ... the result is 0.0 ... instead
>      >> of (what I would get from SAS) of NA (or in the case of
>      >> SAS ".").
>      >>
>      >> Accordingly, I've had to go to 'extreme' measures to get
>      >> the sum function to result in NA if all arguments are
>      >> missing (otherwise give me a sum of all non-NA elements).
>      >>
>      >> So for example here's a snippet of code that ALMOST does
>      >> what I want:
>      >>
>      >>
>      >> SumValue<-apply(subset(InputDataFrame,!is.na(Variable.1)|!is.na(Variable.2),
>      >> select=c(Variable.1,Variable.2)),1,sum,na.rm=TRUE)
>      >>
>      >> In reality this does NOT give me records with NA for
>      >> SumValue ... but it doesn't give me values for any
>      >> records in which both Variable.1 and Variable.2 are NA
>      >> --- which is "good enough" for my purposes.
>      >>
>      >> I'm guessing with a little more work I could come up with
>      >> a way to adapt the code above so that I could get it to
>      >> work like SAS's sum function ...
>      >>
>      >> ... but before I go that extra mile I thought I'd ask
>      >> others if they know of functions in either base R ... or
>      >> in a package that will better mimic the SAS sum function.
>      >>
>      >> Any suggestions?
>      >>
>      >> Thanks.  ______________________________________ Allen
>      >> Bingham aebingham2 at gmail.com
>      >>
>      >> ______________________________________________
>      >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and
>      >> more, see https://stat.ethz.ch/mailman/listinfo/r-help
>      >> PLEASE do read the posting guide
>      >> http://www.R-project.org/posting-guide.html and provide
>      >> commented, minimal, self-contained, reproducible code.
>
>      > ______________________________________________
>      > R-help at r-project.org mailing list -- To UNSUBSCRIBE and
>      > more, see https://stat.ethz.ch/mailman/listinfo/r-help
>      > PLEASE do read the posting guide
>      > http://www.R-project.org/posting-guide.html and provide
>      > commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
Hervé Pagès

Program in Computational Biology
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