Dear Bill,
All makes perfect sense (including the late evaluation). I actually discovered
the problem by looking at old code which used your proposed solution. Still I
find it strange (and, hnestly, I don’t like R’s behavior in this respect), and
I am wondering why u is not being copied to L just before u is assigned a new
value. Of course, this would require the R interpreter to track all these
dependencies in both ways incl. more complicated ones in which L might depend
on more than just u.
In the future, I’ll avoid dependencies between parameters.
Su4 <- function(u=100, l=100, mu=0.53, sigma2=4.3^2) # instead of l=u
And maybe also „in-place“ changes of values…
Best regards,
Matthias
Von: William Dunlap
Gesendet: Samstag, 2. September 2017 19:41
An: Rui Barradas
Cc: Matthias Gondan; r-help@r-project.org
Betreff: Re: [R] Strange lazy evaluation of default arguments
Another way to avoid the problem is to not redefine variables that are
arguments. E.g.,
> Su3 <- function(u=100, l=u, mu=0.53, sigma2=4.3^2, verbose)
{
if (verbose) {
print(c(u, l, mu))
}
uNormalized <- u/sqrt(sigma2)
lNormalized <- l/sqrt(sigma2)
muNormalized <- mu/sqrt(sigma2)
c(uNormalized, lNormalized, muNormalized)
}
> Su3(verbose=TRUE)
[1] 100.00 100.00 0.53
[1] 23.2558140 23.2558140 0.1232558
> Su3(verbose=FALSE)
[1] 23.2558140 23.2558140 0.1232558
Not redefining variables at all makes debugging easier, although it may waste
space.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Sat, Sep 2, 2017 at 10:33 AM, <ruipbarra...@sapo.pt> wrote:
Hello,
One way of preventing that is to use ?force.
Just put
force(l)
right after the commented out print and before you change 'u'.
Hope this helps,
Rui Barradas
Citando Matthias Gondan <matthias-gon...@gmx.de>:
Dear R developers,
sessionInfo() below
Please have a look at the following two versions of the same function:
1. Intended behavior:
Su1 = function(u=100, l=u, mu=0.53, sigma2=4.3^2)
+ {
+ print(c(u, l, mu)) # here, l is set to u’s value
+ u = u/sqrt(sigma2)
+ l = l/sqrt(sigma2)
+ mu = mu/sqrt(sigma2)
+ print(c(u, l, mu))
+ }
Su1()
[1] 100.00 100.00 0.53
[1] 23.2558140 23.2558140 0.1232558
In the first version, both u and l are correctly divided by 4.3.
2. Strange behavior:
Su2 = function(u=100, l=u, mu=0.53, sigma2=4.3^2)
+ {
+ # print(c(u, l, mu))
+ u = u/sqrt(sigma2)
+ l = l/sqrt(sigma2) # here, l is set to u’s value
+ mu = mu/sqrt(sigma2)
+ print(c(u, l, mu))
+ }
Su2()
[1] 23.2558140 5.4083288 0.1232558
In the second version, the print
function is commented out, so the variable u is
copied to l (lowercase L) at a later place, and L is divided twice by 4.3.
Is this behavior intended? It seems strange that the result depends on a
debugging message.
Best wishes,
Matthias
sessionInfo()
R version 3.4.1 (2017-06-30)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)
Matrix products: default
locale:
[1] LC_COLLATE=German_Germany.1252 LC_CTYPE=German_Germany.1252
LC_MONETARY=German_Germany.1252
[4] LC_NUMERIC=C LC_TIME=German_Germany.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
[1] compiler_3.4.1 tools_3.4.1
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______________________________________________
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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.
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______________________________________________
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.
