[R] Bug(?) in predict.tree() --- Evaluation order of Boolean operators

[Peter Dalgaard BSA]

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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