[Rd] ifelse behaviour

[ml-it-r-devel at epigenomics.com]

Duncan Murdoch wrote:
> On 4/26/2007 9:53 AM, ml-it-r-devel at epigenomics.com wrote:
>> Hi!
>>
>> I'm puzzled by the return value of ifelse
>>
>> consider
>>
>> x<-integer(0)
>> ifelse(is(x, "character"), paste(x), x)
>> [1] NA
> 
> The test evaluates to a length 1 logical vector containing FALSE.  So 
> ifelse() tries to return the first entry of x.  But x[1] doesn't exist, 
> so it evaluates to NA, and that's what ifelse() returns.

Thank you for the explanation!

Regards,

   Matthias

>>
>> whereas
>> if (is(x, "character")) return(paste(x)) else x
>> [1] integer(0)
> 
> This is quite different. It says to return the expression in the else 
> clause, which is x.
>>
>> or
>> x<-integer(1)
>> ifelse(is(x, "character"), paste(x), x)
>> [1] 0
>>
>> work as I had anticipated. Is this correct behaviour?
> 
> Yes, this is correct.
> 
> Duncan Murdoch
> 


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