[R] Bug in ifelse

[Rolf Turner]

On 10/10/2008, at 10:33 AM, Daniel Malter wrote:

> Hi all, I am quite sure it's not a bug, but I am going nuts about  
> this. I do
> not possibly understand why I get different results for b1 and b2  
> as shown
> below.
>
> x=c 
> (183,191,192,193,195,206,207,209,210,211,212,213,214,217,218,221,222,2 
> 23,
> 224,225,227,228,229,230)
>
> y=c(221,225,228,241,242)
>
> z=y[y<max(x)] ##all Ys smaller than the maximum of X
>
> a=ifelse(length(z)==0,NA,max(z)) ##assign NA if length of z is  
> zero, take
> the max of z otherwise
>
> b1=ifelse(is.numeric(a)==T,x[x>a],x) ##if a is numeric, assign all  
> x that
> are greater than a; otherwise assign the entire x
>
> b2=x[x>a] ## assign all x greater than a
>
>
> b1 and b2 should be equal as I see it. Anybody who can explain why  
> they are
> not makes my day, especially the one who can tell me how I can get  
> b1 equal
> to b2 (without sacrificing the ifelse condition).

Shouldn't there be an FAQ discussing the difference between ifelse()
and if{ } else { }?  I couldn't find one, and this issue seems to
arise over and OVER again on this list.

Unless their noses are rubbed in it, many people seem not to grok the
distinction.

	cheers,

		Rolf Turner

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