[R] Do NOT use ifelse() if you can use if(.) else . [was "Checking .."]
Ben Tupper
btupper at bigelow.org
Tue Dec 23 19:27:52 CET 2014
On Dec 23, 2014, at 4:05 AM, Martin Maechler <maechler at stat.math.ethz.ch> wrote:
>>>>>> Steven Yen <syen04 at gmail.com>
>>>>>> on Sun, 14 Dec 2014 09:30:56 -0500 writes:
>>>>>> Steven Yen <syen04 at gmail.com>
>>>>>> on Sun, 14 Dec 2014 09:30:56 -0500 writes:
>
>> Thanks. This worked!! :)
>> Fisher <- ifelse(!("Fisher" %in% names(obj$spec)), FALSE, obj$spec$Fisher)
>
> "worked", yes.
>
> But please --- for the mailing list archives ---
> do use better code.
>
> Unfortunately, ifelse() is used and has been advertized much too
> often in cases where it is very sub-optimal efficiency wise.
> ifelse(Cond, A, B) should only be used when the condition
> 'Cond', a logical vector can be (and typically is) of length > 1
> {and even then, it maybe a nice short cut, but often still suboptimal
> efficiency wise ... but let's not get there}
>
> In cases like this one when the condition 'Cond' is a
> simple TRUE or FALSE (i.e. of length 1), using
>
> if(Cond) A else B
>
> instead of
>
> ifelse(Cond, A, B)
>
> is
>
> 1. much more R - like [[ "everything you do is a function call" ]]
> hence much more elegant
>
> 2. considerably more efficient.
>
> 3. :-) less typing: uses two "," less ;-)
>
>> require(microbenchmark)
> Loading required package: microbenchmark
>> x <- setNames(,LETTERS)
>> y <- setNames(letters, runif(letters))
>> z <- pi
>> microbenchmark(r1 <- ifelse(z > 3, x, y), r2 <- if(z > 3) x else y, times=1000)
> Unit: nanoseconds
> expr min lq mean median uq max neval cld
> r1 <- ifelse(z > 3, x, y) 4466 4971.5 5498.928 5244 5673.5 31705 1000 b
> r2 <- if (z > 3) x else y 171 212.0 265.241 264 291.0 3130 1000 a
>>
>
> i.e., roughly a factor of 20 times more efficient
>
Wow! This is great, and I had no idea I was misusing ifelse.
Thanks!
Ben
>
> Martin Maechler,
> ETH Zurich and R Core Team.
>
>
>> At 08:43 AM 12/14/2014, Ben Tupper wrote:
>>> Hi,
>>>
>>> Does this work for you? It simply tests if the name Fisher is found
>>> among the names of the elements of spec.
>>>
>>> obj = list(spec = list)
>>> Fisher <- ifelse(!("Fisher" %in% names(obj$spec)), FALSE, obj$spec$Fisher)
>>>
>>> Cheers,
>>> Ben
>>>
>>> On Dec 14, 2014, at 8:07 AM, Steven Yen <syen04 at gmail.com> wrote:
>>>
>>>> My obj does not always come with a logical variable defined. So I do
>>>>
>>>> my.foo <- function(obj,df,digits=5){
>>>> if (!is.na("obj$spec$Fisher")) Fisher<-obj$spec$Fisher
>>>> ...
>>>> }
>>>>
>>>> This works when "Fisher" is defined in/passed from obj. When it
>>> is not, I get error:
>>>>
>>>> Error in (!is.na("obj$spec$Fisher")) & Fisher :
>>>> operations are possible only for numeric, logical or complex types
>>>>
>>>> I tried exist(Fisher), missing(Fisher)... to no vail. Any idea? Thanks.
Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org
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