[R] That dreaded floating point trap

[Alexander Engelhardt]

Hi,
I had a piece of code which looped over a decimal vector like this:


for( i in where ){
   thisdata <- subset(herde, herde$mlr >= i)
   # do stuff with thisdata..
}

'where' is a vector like seq(-1, 1, by=0.1)

My problem was: 'nrow(thisdata)' in loop repetition 0.4 was different if 
'where' was seq(-1, 1, by=0.1) than when 'where' was seq(-0.8, 1, by=0.1)
It went away after I changed the first line to:

   thisdata <- subset(herde, herde$mlr >= round(i, digits=1))

This is that "floating point trap" the R inferno pdf talked about, 
right? That file talked about the problem, but didn't offer a solution.

Similar things happened when I created a table() from a vector with 
values in seq(-1, 1, by=0.1)

Do I really have to round every float at every occurence from now on, or 
is there another solution? I only found all.equal() and identical(), but 
I want to subset for observations with a value /greater/ than something.

Thanks in advance,
  Alex