different type of modification when code is sourced and pasted

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different type of modification when code is sourced and pasted

Krzysztof Bartoszek
Dear all,
I have a question about R's modification in place and replacement functions.
I was working through Hadley Wickham's Advanced R section on
Replacement Functions and
in a file (say test.R) I wrote:

`second<-` <- function(x, value) {
   x[2] <- value
   x
}
x <- 1:10
second(x) <- 5L
print(x)

library(pryr)
x <- 1:10
print(address(x))
second(x) <- 6L
print(address(x))
x <- 1:10
print(address(x))
x[2] <- 7L
print(address(x))

When I copy-paste the code the effect is as expected:
> `second<-` <- function(x, value) {
+    x[2] <- value
+    x
+ }
> x <- 1:10
> second(x) <- 5L
> print(x)
 [1]  1  5  3  4  5  6  7  8  9 10
>
> library(pryr)
> x <- 1:10
> print(address(x))
[1] "0x1b44ef40"
> second(x) <- 6L
> print(address(x))
[1] "0x1f955a38"
> x <- 1:10
> print(address(x))
[1] "0x1b447090"
> x[2] <- 7L
> print(address(x))
[1] "0x1b447090"

However, when I source the code the effect is a bit surprising:
> source("test.R")
 [1]  1  5  3  4  5  6  7  8  9 10
[1] "0x2f372320"
[1] "0x2f394888"
[1] "0x1b446ef0"
[1] "0x1f960f30"
Notice, that the last two addresses are different.
I would be grateful if somebody could point me to an explanation for this.
I have tried this on: R version 3.1.2 running on openSUSE 12.1, R
version 3.4.2 running on openSUSE Leap 42.3
and on R running on a friend's Mac.

Thank you
Best wishes
Krzysztof Bartoszek

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Re: different type of modification when code is sourced and pasted

luke-tierney
Basically as a result of all the bells and whistles source() supports
it ends up creating an additional reference to the value of each top
level expression. That forces a duplicate.

Best,

luke

On Sun, 13 May 2018, Krzysztof Bartoszek wrote:

> Dear all,
> I have a question about R's modification in place and replacement functions.
> I was working through Hadley Wickham's Advanced R section on
> Replacement Functions and
> in a file (say test.R) I wrote:
>
> `second<-` <- function(x, value) {
>   x[2] <- value
>   x
> }
> x <- 1:10
> second(x) <- 5L
> print(x)
>
> library(pryr)
> x <- 1:10
> print(address(x))
> second(x) <- 6L
> print(address(x))
> x <- 1:10
> print(address(x))
> x[2] <- 7L
> print(address(x))
>
> When I copy-paste the code the effect is as expected:
>> `second<-` <- function(x, value) {
> +    x[2] <- value
> +    x
> + }
>> x <- 1:10
>> second(x) <- 5L
>> print(x)
> [1]  1  5  3  4  5  6  7  8  9 10
>>
>> library(pryr)
>> x <- 1:10
>> print(address(x))
> [1] "0x1b44ef40"
>> second(x) <- 6L
>> print(address(x))
> [1] "0x1f955a38"
>> x <- 1:10
>> print(address(x))
> [1] "0x1b447090"
>> x[2] <- 7L
>> print(address(x))
> [1] "0x1b447090"
>
> However, when I source the code the effect is a bit surprising:
>> source("test.R")
> [1]  1  5  3  4  5  6  7  8  9 10
> [1] "0x2f372320"
> [1] "0x2f394888"
> [1] "0x1b446ef0"
> [1] "0x1f960f30"
> Notice, that the last two addresses are different.
> I would be grateful if somebody could point me to an explanation for this.
> I have tried this on: R version 3.1.2 running on openSUSE 12.1, R
> version 3.4.2 running on openSUSE Leap 42.3
> and on R running on a friend's Mac.
>
> Thank you
> Best wishes
> Krzysztof Bartoszek
>
> ______________________________________________
> [hidden email] mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

--
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:   [hidden email]
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu

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