[R] Printout and saved results

[Ben Bolker]

   Fragile and probably a bad idea, but:

"%.%" <- function(x,y) { assign(deparse(substitute(x)), y, 
parent.frame()); print(y) }


   > a %.% "hello"
   [1] "hello"
   > a
   [1] "hello"

  Not sure how much value this has over other idioms such as wrapping 
the assignment in parentheses, which makes the result into a new 
expression, which is then printed:

(a <- "hello")
[1] "hello"

On 2024-03-26 8:39 a.m., avi.e.gross using gmail.com wrote:
> Just FYI, the R interpreter typically saves the last value returned briefly
> in a variable called .Last.value that can be accessed before you do anything
> else.
> 
>> sin(.5)
> [1] 0.4794255
>> temp <- .Last.value
>> print(temp)
> [1] 0.4794255
>> sin(.666)
> [1] 0.6178457
>> .Last.value
> [1] 0.6178457
>> temp
> [1] 0.4794255
>> invisible(sin(0.2))
>> .Last.value
> [1] 0.1986693
> 
> So perhaps if you grab it in time, you can call your function and let the
> REPL display it (or not) and yet save the value.
> 
> 
> 
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Jeff Newmiller via
> R-help
> Sent: Tuesday, March 26, 2024 1:03 AM
> To: r-help using r-project.org
> Subject: Re: [R] Printout and saved results
> 
> Your desire is not unusual among novices... but it is really not a good idea
> for your function to be making those decisions. Look at how R does things:
> 
> The lm function prints nothing... it returns an object containing the result
> of a linear regression. If you happen to call it directly from the R command
> prompt and don't assign it to a variable, then the command interpreter
> notices that return value and prints it. Since the lm object has a dedicated
> print method associated with it, that output looks different than a plain
> list object would... but the fact that it has a special print method
> (?print.lm) is just window dressing unrelated to your request.
> 
> The important part is that the lm function doesn't even consider printing
> anything out... it is the code that calls the function that determines
> whether it will get printed. So...
> 
> lm( hp ~ disp, data = mtcars )  # printed by command interpreter
> z <- lm( hp ~ disp, data = mtcars ) # assignment operator returns the value
> of z to the command processor, but invisibly
> ( z <- lm( hp ~ disp, data = mtcars ) ) # strips off the invisible marking
> so the value gets printed
> 
> Another example:
> 
> f <- function() {
>    x <- 4
>    x  # doesn't print
>    invisible( 5 ) # return invisible result
> }
> 
> f()  # doesn't print 4 because there is no command prompt looking at x alone
> on a line... it is inside f
> # command prompt doesn't print 5 because that 5 has been marked as invisible
> (f()) # command interpreter prints 5
> 
> Leaving it up to the calling code to decide whether to print gives you the
> option of calling your analysis function possibly thousands of times and
> figuring out some slick way to summarize all those runs without thousands of
> printouts that you are not going to wade through anyway and would only slow
> the computer down (printing really does slow the computer down!)
> 
> 
> On March 25, 2024 9:00:49 PM PDT, Steven Yen <styen using ntu.edu.tw> wrote:
>> I just like the subroutine to spit out results (Mean, Std.dev, etc.) and
> also be able to access the results for further processing, i.e.,
>>
>> v$Mean
>>
>> v$Std.dev
>>
>> On 3/26/2024 11:24 AM, Richard O'Keefe wrote:
>>> Not clear what you mean by "saved".
>>> If you call a function and the result is printed, the result is
>>> remembered for a wee while in
>>> the variable .Last.value, so you can do
>>>> function.with.interesting.result(.......)
>>>> retained.interesting.result <- .Last.value
>>> or even
>>>> .Last.value -> retained.interesting.result
>>> If you know before you start writing the expression that you want to
>>> save the value,
>>> you can wrap the assignment in parentheses, making it an expression:
>>>
>>>> (retained.interesting.result <-
> function.with.interesting.result(......))
>>>
>>> On Tue, 26 Mar 2024 at 15:03, Steven Yen <styen using ntu.edu.tw> wrote:
>>>> How can I have both printout and saved results at the same time.
>>>>
>>>> The subroutine first return "out" and the printout gets printed, but not
>>>> saved.
>>>>
>>>> I then run the "invisible" line. Results got saved and accessible but no
>>>> printout.
>>>>
>>>> How can I have both printout and also have the results saved? Thank you!
>>>>
>>>>    > dstat4 <- function(data,digits=3){
>>>> +   Mean    <- apply(data,2,mean,na.rm=TRUE)
>>>> +   Std.dev <- apply(data,2,sd,  na.rm=TRUE)
>>>> +   Min <- apply(data,2,min,na.rm=TRUE)
>>>> +   Max <- apply(data,2,max,na.rm=TRUE)
>>>> +   Obs <- dim(data)[1]
>>>> +   out <-round(cbind(Mean,Std.dev,Min,Max,Obs),digits)
>>>> +   out
>>>> + # invisible(list(Mean=Mean,Std.dev=Std.dev,Min=Min,Max=Max))
>>>> + }
>>>>    > x1<-rnorm(n=5,mean=5, sd=1)
>>>>    > x2<-rnorm(n=5,mean=10,sd=2)
>>>>    > w<-rnorm(n=5,mean=2,sd=0.3)
>>>>    > mydata<-data.frame(cbind(x1,x2))
>>>>    > v<-dstat4(mydata); v
>>>>         Mean Std.dev   Min    Max Obs
>>>> x1  5.000   0.922 3.900  6.282   5
>>>> x2 10.769   1.713 9.209 13.346   5
>>>>    > v$Mean
>>>> Error in v$Mean : $ operator is invalid for atomic vectors
>>>>    > dstat4 <- function(data,digits=3){
>>>> +   Mean    <- apply(data,2,mean,na.rm=TRUE)
>>>> +   Std.dev <- apply(data,2,sd,  na.rm=TRUE)
>>>> +   Min <- apply(data,2,min,na.rm=TRUE)
>>>> +   Max <- apply(data,2,max,na.rm=TRUE)
>>>> +   Obs <- dim(data)[1]
>>>> +   out <-round(cbind(Mean,Std.dev,Min,Max,Obs),digits)
>>>> + # out
>>>> +   invisible(list(Mean=Mean,Std.dev=Std.dev,Min=Min,Max=Max))
>>>> + }
>>>>
>>>>    > v<-dstat4(mydata)
>>>>    > v$Mean
>>>>          x1       x2
>>>> 4.233051 9.564454
>>>>
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>>
>> ______________________________________________
>> R-help using 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.
>