R help - Nov 2008 - Variable passed to function not used in function in select=... in subset

Hello!

I have the problem that in my function the passed variable is not used, but the
variable name of the dataframe itself?- difficult to explain, but an easy
example:

TestFunc<-function(df, group) {
??? print(names(subset(df, select=group)))
}
df1<-data.frame(group="G1", visit="V1", value=0.9)
TestFunc(df1, c("group", "visit"))

Result:
[1] "group"
?
But I expected and want to have [1] "group" "visit" as
result! Does anybody know how to?get this result?

Thanks!
Karl

Try this:

TestFunc<-function(df, group) {
    return(names(eval(bquote(subset(df1, select = .(group))))))
}

On Mon, Nov 10, 2008 at 1:18 PM, Karl Knoblick
<karlknoblich@yahoo.de>wrote:
> Hello!
>
> I have the problem that in my function the passed variable is not used, but
> the variable name of the dataframe itself - difficult to explain, but an
> easy example:
>
> TestFunc<-function(df, group) {
>     print(names(subset(df, select=group)))
> }
> df1<-data.frame(group="G1", visit="V1", value=0.9)
> TestFunc(df1, c("group", "visit"))
>
> Result:
> [1] "group"
>
> But I expected and want to have [1] "group" "visit" as
result! Does anybody
> know how to get this result?
>
> Thanks!
> Karl
>
>
>
>
> ______________________________________________
> R-help@r-project.org mailing list
> 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.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

On 11/10/2008 10:18 AM, Karl Knoblick wrote:
> Hello!
> 
> I have the problem that in my function the passed variable is not used, but
the variable name of the dataframe itself - difficult to explain, but an easy
example:
> 
> TestFunc<-function(df, group) {
>     print(names(subset(df, select=group)))
> }
> df1<-data.frame(group="G1", visit="V1", value=0.9)
> TestFunc(df1, c("group", "visit"))
> 
> Result:
> [1] "group"
>  
> But I expected and want to have [1] "group" "visit" as
result! Does anybody know how to get this result?
Don't use subset.  You can get what you want using


print(names(df[,group]))

Or alternatively, you can force group to be found in the right place in 
this way:

e <- environment()
print(names(subset(df, select=e$group)))

Here are a few things to try:

TestFunc1 <- get("[")

TestFunc2 <- function(DF, group) DF[group]

TestFunc3 <- function(...) subset(..., subset = TRUE)



On Mon, Nov 10, 2008 at 10:18 AM, Karl Knoblick <karlknoblich at yahoo.de>
wrote:
> Hello!
>
> I have the problem that in my function the passed variable is not used, but
the variable name of the dataframe itself - difficult to explain, but an easy
example:
>
> TestFunc<-function(df, group) {
>     print(names(subset(df, select=group)))
> }
> df1<-data.frame(group="G1", visit="V1", value=0.9)
> TestFunc(df1, c("group", "visit"))
>
> Result:
> [1] "group"
>
> But I expected and want to have [1] "group" "visit" as
result! Does anybody know how to get this result?
>
> Thanks!
> Karl
>
>
>
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
>

Forgot the name part.  Try:

TestFunc2 <- function(DF, group) names(DF[group])
TestFunc3 <- function(...) names(subset(..., subset = TRUE))
TestFunc4 <- function(...) eval.parent(names(subset(..., subset = TRUE)))

# e.g.
df1 <- data.frame(group = "G1", visit = "V1", value =
0.9)
TestFunc2(df1, c("group", "visit"))
TestFunc3(df1, c("group", "visit"))
TestFunc4(df1, c("group", "visit"))
TestFunc4(df1, c(group, visit)) # this works too

On Mon, Nov 10, 2008 at 10:43 AM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> Here are a few things to try:
>
> TestFunc1 <- get("[")
>
> TestFunc2 <- function(DF, group) DF[group]
>
> TestFunc3 <- function(...) subset(..., subset = TRUE)
>
>
>
> On Mon, Nov 10, 2008 at 10:18 AM, Karl Knoblick <karlknoblich at
yahoo.de> wrote:
>> Hello!
>>
>> I have the problem that in my function the passed variable is not used,
but the variable name of the dataframe itself - difficult to explain, but an
easy example:
>>
>> TestFunc<-function(df, group) {
>>     print(names(subset(df, select=group)))
>> }
>> df1<-data.frame(group="G1", visit="V1",
value=0.9)
>> TestFunc(df1, c("group", "visit"))
>>
>> Result:
>> [1] "group"
>>
>> But I expected and want to have [1] "group" "visit"
as result! Does anybody know how to get this result?
>>
>> Thanks!
>> Karl
>>
>>
>>
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> 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.
>>
>

Gavin Simpson wrote:
>
> I've found several of these discussions involving Wacek's questions
very
> enlightening at times; once you get past the "it doesn't work as I
> expect so is wrong" attitude.
>   
just one fix:  my attitude is 'it doesn't work as i imagine an average
user would expect it so it's potentially confusing'.

vQ



-- 
-------------------------------------------------------------------------------
Wacek Kusnierczyk, MD PhD

Email: waku at idi.ntnu.no
Phone: +47 73591875, +47 72574609

Department of Computer and Information Science (IDI)
Faculty of Information Technology, Mathematics and Electrical Engineering (IME)
Norwegian University of Science and Technology (NTNU)
Sem Saelands vei 7, 7491 Trondheim, Norway
Room itv303

Bioinformatics & Gene Regulation Group
Department of Cancer Research and Molecular Medicine (IKM)
Faculty of Medicine (DMF)
Norwegian University of Science and Technology (NTNU)
Laboratory Center, Erling Skjalgsons gt. 1, 7030 Trondheim, Norway
Room 231.05.060

Some of the uses of non-standard evaluation are undoubtedly a problem in 
R. Probably the worst is in model.frame, because it is much harder to 
work around. I have never used subset(,select=) and hence have never 
been at risk of confusion (if you don't like how it works, I suggest you 
do the same), but model.frame() is inside lots of things.

  There are two issues here that I think are worth pointing out:
1/ Some things are just not fixable any more. They can only be fixed in a 
new language. The people thinking about new statistical languages mostly 
know what the problems are, because they have been using S and/or R for 
many years and it's really not that hard to notice the problems. The 
document on non-standard evaluation demonstrates that R-core is aware of 
this particular problem.

2/ There are some uses of non-standard evaluation that don't seem to 
confuse people, and an interesting question is how to characterise them. 
These are what I referred to as 'macro-like functions' in the document 
that you have already been referred to.  For example, subset(,subset=) and 
with() don't seem to be as confusing or to cause problems for programmers 
in the same way. There is an empirical question as to what these 
relatively non-problematic constructs are, and a theoretical question as 
to why they are different. In particular, with() not only has non-standard 
evaluation, it is quite similar to the notoriously confusing attach().


 	-thomas


On Tue, 11 Nov 2008, Wacek Kusnierczyk wrote:
> Berwin A Turlach wrote:
>> On Tue, 11 Nov 2008 09:27:41 +0100
>> Wacek Kusnierczyk <Waclaw.Marcin.Kusnierczyk at idi.ntnu.no>
wrote:
>>
>>
>>> but then it might be worth asking whether carrying on with
misdesign
>>> for backward compatibility outbalances guaranteed crashes in future
>>> users' programs, [...]
>>>
>>
>> Why is it worth asking this if nobody else asks it?
>
>
> i guess most of the people who do ask questions here care little about r
> itself, they just want it to solve a problem, even if it involves
> hacking the language.
>
> those outside the r team who care about language design have probably
> left the list long ago, if only they were subscribed.  the fact that
> it's only me asking is no statistics.  i do talk to people, and know
> many who'd ask, but they just don't care, because they have already
> trashed r.  instead of discouraging me, make use of that i care to ask.
>
> vQ
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
>
Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle