David et. al.:
"this levels is the level where you realize that the `for` function is
different from most other R functions. It is really a
side-effect-fucntion. "
for(), while(), if(), next, etc. are *not* functions.
?for says: "These are the basic control-flow constructs of the R language."
They do not "return" values. They control program flow, whence what
you call "side effects" are actually expressions that are parsed and
evaluated
viz.
> if(TRUE)10
[1] 10
## but
>if(FALSE) 5
## nothing is returned, not even NULL
> for(i in 1:3) i
## Ditto
> z <- NULL
> z <- for(i in 1:3)i
> z
NULL ## still
Cheers,
Bert
Cheers,
Bert
Bert Gunter
"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
On Sun, Apr 16, 2017 at 8:12 PM, David Winsemius <dwinsem...@comcast.net> wrote:
>
>> On Apr 16, 2017, at 7:26 PM, Ramnik Bansal <ramnik.ban...@gmail.com> wrote:
>>
>> In the code below
>>
>>
>> *ff <- function(n){ for(i in 1:n) (i+1)}*
>>
>> *n<-3;ff(n)->op;print(op)*
>>
>> Why doesnt *print(op) * print 4 and instead prints NULL.
>> Isnt the last line of code executed is *i+1 * and therefore that should be
>> returned instead of NULL
>>
>> instead if I say
>> *ff <- function(n){ (n+1) }*
>>
>> Then
>> *n<-3;ff(n)->op;rm(n);print(op)*
>> gives 4 as output.
>>
>> My question is *Which *is considered as the last line in a functoin for the
>> purpsoe of default return ? And under what conditions ?
>
> It's probably a good thing that you are confused. It suggests that you are
> actually "getting" the R-paradigm. Unfortunately for the new user of R, there
> are several levels of understanding to pass through. First, you realize that
> function-results need to be assigned to names in order to persist. Then there
> is the next level where you discover that there are exceptions to that rule:
> this levels is the level where you realize that the `for` function is
> different from most other R functions. It is really a side-effect-fucntion.
> The assignments made within its body actually persist in the global
> environment. AND it returns NULL. It shares this anomalous behavior with
> `while` and `repeat`.n Almost all functions are invoked with a possibly empty
> argument list. The next and break functions have implicit paired (empty)
> parentheses.
>
> (My personal opinion is that this is not adequately advertised. Perhaps it is
> an attempt to get people to migrate away from "Fortran-coding" behavior?)
>
> --
> David.
>
>
>>
>> -Thanks,
>> Ramnik
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius
> Alameda, CA, USA
>
> ______________________________________________
> R-help@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.
______________________________________________
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