Damn scoping in R

February 17, 2011
By

(This article was first published on binfalse » R, and kindly contributed to R-bloggers)

Ok, R is very well-considered in certain respects, but there are also some things annoying me… This time it’s scoping…

Let’s have a look to the following code:

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fun=function()
{
    if (runif(1) > .5)
        x = 1
    x
}

First it looks damn unspectacular. But wait, whats that:

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> x=0
> fun()
[1] 1
> fun()
[1] 0

Taking a closer look to the function shows that the returned value is randomly chosen from local (runif(1) > .5) or global scope (runif(1) <= .5). So you can’t expect a result from this function. Nasty, especially while debugging external code, isn’t it? :-)

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> sum(sapply(1:10^6, function (null) fun()))/10^6
[1] 0.499681

So again my advise: Think about such specific features! This won’t happen in any sensible language…

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