[R] A suggestion to improve ifelse behaviour with vector yes/no arguments

Duncan Murdoch murdoch at stats.uwo.ca
Tue May 31 21:14:10 CEST 2005

Thomas Lumley wrote:
> On Tue, 31 May 2005, Duncan Murdoch wrote:
>>Mäkinen Jussi wrote:
>>>Dear All,
>>>I luckily found the following feature (or problem) when tried to apply 
>>>ifelse-function to an ordered data.
>>>>ifelse(test, 0, 1:4)
>>>[1] 0 0 0 4 1 2 3
> <snippage>
>>As Dimitris said, this is just recycling.  I think getting rid of recycling 
>>on vectors with length greater than 1 would have been a good decision in S 
>>about 15 years ago, but it's too late now.
> It wouldn't help the original poster, though.  I agree that 0,0,0,4,1,2,3 
> is a slightly weird result, but I can't think of any reasonable model for 
> the behaviour of ifelse() that would give any other result except an error 
> message. [or  0,NA,NA,4,NA,NA,NA, I suppose].

I would vote for the error message.  I can't think of a single example 
where a vector of length 7 is needed, and a vector of length 4 is 
recycled to give it, that *doesn't* give a slightly weird result.

Maybe this is something that should have been changed in R 2.0.0; we 
squandered that change from 1.x.x to 2.x.x.

Duncan Murdoch

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