[R] Return value from function with For loop

[Ramnik Bansal]

This is my output for is.function

> is.function("for")
[1] FALSE
> is.function(for)
Error: unexpected ')' in "is.function(for)"
> is.function("next")
[1] FALSE
> is.function(next)
Error: no loop for break/next, jumping to top level

*I did not get the TRUE value. R version 3.3.3 on Mac. What am I doing
different ?*

Packages detail
> search()
 [1] ".GlobalEnv"        "package:pryr"
 [3] "tools:RGUI"        "package:stats"
 [5] "package:graphics"  "package:grDevices"
 [7] "package:utils"     "package:datasets"
 [9] "package:methods"   "Autoloads"
[11] "package:base"

thanks
Ramnik

On Mon, Apr 17, 2017 at 12:06 PM, David Winsemius <dwinsemius at comcast.net>
wrote:

> Both 'for' and 'next' return TRUE from is.function
>
> is.function('for')
> is.function('next')
>
> Not at an R console at the moment but I did check this earlier today.
> Thinking of it as different is definitely the way to think about it. (ISTR
> Bert and I have had this exchange in the past.)
>
> --
> Best
> David
>
> Sent from my iPhone
>
> > On Apr 16, 2017, at 9:50 PM, Bert Gunter <bgunter.4567 at gmail.com> wrote:
> >
> > 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 <
> dwinsemius at comcast.net> wrote:
> >>
> >>> On Apr 16, 2017, at 7:26 PM, Ramnik Bansal <ramnik.bansal at 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 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.
> >>
> >> David Winsemius
> >> Alameda, CA, USA
> >>
> >> ______________________________________________
> >> 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.
>
>

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