weird [lack of] control…

February 20, 2012

(This article was first published on Xi'an's Og » R, and kindly contributed to R-bloggers)

When I ran

> test=NULL
> for (i in 1:10){
+   if (i%%2!=0){
+     test=c(test,i)
+     i=i+2}}
> test
[1] 1 3 5 7 9

I was expecting the same output as

> test=NULL
> i=1
> while (i test
[1] 1 5 9

So this means that the dummy index in R “for” loops cannot be tweaked that easily. I seem to remember doing this kind of (dirty) tricks with earlier versions… Now, Alessandra and Robin think this is a good thing that the for loop is robust against this kind of non-sense, so I may be a minority in complaining about this lack of control [for me, if not for for].

Filed under: R, University life Tagged: dummy variable, for loop, loops, R