Hi David,
Thanks for the correction concerning the "else" issue.
Taking your code and removing some lines (to increase readability):
library(pryr)
data <- array(dim = c(5))
for(x in 1:5)
{
data[x] <- as.integer(x * 2)
}
#print(data)
add = address(data)
for(x in 1:5)
{
data[x] <- as.integer(0)
}
if (add == address(data))
{
print("Address did not change")
} else {
print("Address changed")
}
If one runs this code everything works as expected, i.e. message "Address did
not change" is printed. However, if one uncomments line "#print(data)", message
"Address is changed" is printed instead. Any idea why this happens as it is a
bit counter-intuitive? Is it something to do with some kind of lazy-evaluation
mechanism R has that makes the array to be filled-up only when needed (in this
case, when printing it) thus changing the array's address?
Thank you once more!
Sent: Sunday, November 12, 2017 at 6:02 PM
From: "David Winsemius" <dwinsem...@comcast.net>
To: "lille stor" <lille.s...@gmx.com>
Cc: r-devel@r-project.org
Subject: Re: [Rd] Array changing address unexpectedly
> On Nov 12, 2017, at 8:47 AM, lille stor <lille.s...@gmx.com> wrote:
>
> Hi,
>
> Given the following R code:
>
> library(pryr)
>
> data <- array(dim = c(5))
>
> for(x in 1:5)
> {
> data[x] <- as.integer(x * 2)
> }
>
> add = address(data) # save address of "data"
>
> for(x in 1:5)
> {
> data[x] <- as.integer(0)
> }
>
> if (add == address(data))
> {
> print("Address did not change")
> }
> else
> {
> print("Address changed")
> }
>
> If one runs this code, message "Address changed" is printed. However, if one
> comments line "data[x] <- as.integer(0)" the address of "data" does not
> change and message "Address did not change" is printed instead. Why? The
> datatype of the array should not change with this line and hence no need for
> R to convert the array to a different type (and have the array's address
> changing in the process).
I'm guessing you didn't take note of the error message:
> else
Error: unexpected 'else' in " else"
It's always good practice to investigate errors. The else function needs to
come immediately after the "{".
Here's a more complete test of what I take to be your question:
library(pryr)
data <- array(dim = c(5))
add = address(data)
for(x in 1:5)
{
data[x] <- as.integer(x * 2)
}
if (add == address(data))
{
print("Address did not change")
} else {
print("Address changed")
}
data <- array(dim = c(5)) # reset
add = address(data)
for(x in 1:5)
{
data[x] <- as.integer(0)
}
if (add == address(data))
{
print("Address did not change")
} else {
print("Address changed")
}
# changes in both situations.
>
> Thank you!
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
David Winsemius
Alameda, CA, USA
'Any technology distinguishable from magic is insufficiently advanced.' -Gehm's
Corollary to Clarke's Third Law
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