R help - Feb 2002 - Bug(?) in predict.tree() --- Evaluation order of Boolean operators

Dear R users

I have a problem with predict.tree() when I want the fitted values
of a tree object to be returned (i.e. argument 'newdata' is missing). 
Whatever I specify for argument 'type' the fitted model object is 
returned.

Example:
   library(tree)
   data(kyphosis)
   fit.tree <- tree(Kyphosis ~ Age + Number + Start, data=kyphosis)

   p <- predict(fit.tree, type="class")
   class(p)
   [1] "tree"

I expected p to be a factor with levels absent or present.

Note that S-Plus has (almost) the same code for predict.tree()
and gives
   > class(p)
   [1] "factor"
   > p
   [1] absent  absent  present absent  absent  absent  absent  absent
       [...]
   [79] absent  present absent 


I think the source of the problem is located in the following lines
of predict.tree():
   if (missing(newdata) || is.null(newdata) & type == "tree") 
       return(object)

When  missing(newdata)  is TRUE the logical expression
   missing(newdata) || is.null(newdata) & type == "tree"
is always TRUE, whatever is.null(newdata) or type == "tree" are:
   TRUE || FALSE & FALSE
   [1] TRUE

Note that S-Plus 6 for Windows gives
   TRUE || FALSE & FALSE
   [1] F

I don't want to judge which one is correct.

Btw. I use 
> version
         _              
platform i386-pc-mingw32
arch     x86            
os       Win32          
system   x86, Win32     
status                  
major    1              
minor    4.1            
year     2002           
month    01             
day      30             
language R   

------------------------------------------

Christian Keller
===============UBS AG
Analytical CRM UBS CH
N?schelerstrasse 22, CH-8098 Z?rich
Tel. +41-1-234 51 48, Fax. +41-1-234 26 83
christian-za.keller at ubs.com

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christian-za.keller at ubs.com writes:
> I think the source of the problem is located in the following lines
> of predict.tree():
>    if (missing(newdata) || is.null(newdata) & type == "tree")
>        return(object)
> 
> When  missing(newdata)  is TRUE the logical expression
>    missing(newdata) || is.null(newdata) & type == "tree"
> is always TRUE, whatever is.null(newdata) or type == "tree" are:
>    TRUE || FALSE & FALSE
>    [1] TRUE
> 
> Note that S-Plus 6 for Windows gives
>    TRUE || FALSE & FALSE
>    [1] F
> 
> I don't want to judge which one is correct.
It's an operator precedence issue. || has higher precedence than & in
S (-plus, 6.0 and 3.4), but lower in R.

Try substitute(T||F&F)[[1]]

I think we want to be compatible, but we'll not likely change it in
the 1.4.x series. However, a set of parentheses should help...

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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Dear Peter 

Thank you for your help.
>> It's an operator precedence issue. || has higher precedence than
& in
>> S (-plus, 6.0 and 3.4), but lower in R.
>>
>> Try substitute(T||F&F)[[1]]
>>
>> I think we want to be compatible, but we'll not likely change it in
>> the 1.4.x series. However, a set of parentheses should help...
Note also that in R:
   > T || F & F
   [1] TRUE
   > F & F || T
   [1] TRUE
   > substitute(T || F & F)[[1]]
   ||
   > substitute(F & F || T)[[1]]
   ||

while in S-Plus:
   > T || F & F
   [1] F
   > F & F || T
   [1] T
   > substitute(T || F & F)[[1]]
    & 
   > substitute(F & F || T)[[1]]
    || 


Christian

------------------------------------------
Christian Keller
===============UBS AG
Analytical CRM UBS CH
N?schelerstrasse 22, CH-8098 Z?rich
Tel. +41-1-234 51 48, Fax. +41-1-234 26 83
christian-za.keller at ubs.com

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> || has higher precedence than & in S (-plus, 6.0 and 3.4), but lower
in R.

Actually, in all versions of S-PLUS (as documented in ?Syntax and
following the Blue Book), ||, |, & and && all have the same
precedence
and hence are evaluated left to right.  This explains Christian's
results.

-- 
David M Smith <dsmith at insightful.com>
S-PLUS Product Marketing Manager, Insightful Corp, Seattle WA
Tel: +1 (206) 802 2360
Fax: +1 (206) 283 6310

Insightful Corporation provides analytical solutions leveraging
S-PLUS, StatServer, S-PLUS Analytic Server and consulting services.
See www.insightful.com for details. 
> -----Original Message-----
> From: christian-za.keller at ubs.com [mailto:christian-za.keller at
ubs.com]
> Sent: Friday, February 15, 2002 08:32
> To: p.dalgaard at biostat.ku.dk
> Cc: r-help at stat.math.ethz.ch
> Subject: RE: Re: [R] Bug(?) in predict.tree() --- Evaluation order of
> Boolean operators
> 
> 
> Dear Peter 
> 
> Thank you for your help.
> 
> >> It's an operator precedence issue. || has higher 
> precedence than & in
> >> S (-plus, 6.0 and 3.4), but lower in R.
> >>
> >> Try substitute(T||F&F)[[1]]
> >>
> >> I think we want to be compatible, but we'll not likely change
it in
> >> the 1.4.x series. However, a set of parentheses should help...
> 
> Note also that in R:
>    > T || F & F
>    [1] TRUE
>    > F & F || T
>    [1] TRUE
>    > substitute(T || F & F)[[1]]
>    ||
>    > substitute(F & F || T)[[1]]
>    ||
> 
> while in S-Plus:
>    > T || F & F
>    [1] F
>    > F & F || T
>    [1] T
>    > substitute(T || F & F)[[1]]
>     & 
>    > substitute(F & F || T)[[1]]
>     || 
> 
> 
> Christian
> 
> ------------------------------------------
> Christian Keller
> ===============> UBS AG
> Analytical CRM UBS CH
> N?schelerstrasse 22, CH-8098 Z?rich
> Tel. +41-1-234 51 48, Fax. +41-1-234 26 83
> christian-za.keller at ubs.com
> 
> -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
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> http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
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> _._._._._._._._._
> 
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