To round or not to round… [Software]

posted by ElMaestro  – Belgium?, 2019-07-20 19:59 (457 d 12:42 ago) – Posting: # 20415
Views: 4,683

Hi Hötzi,

» I don’t know which kind of measurements you are comparing.

It stinks but there really is no good solution when you have to compare.
(294.1/1000) == 0.2941
[1] FALSE
(2941/10000) == 0.2941
[1] TRUE


One can read ISO standards and manuals about internal float representation (I tried andfell asleep), but at the end of the day if you need to compare you need to compare and hope for the best. Some numbers just cannot be represented accurately in binary.

If you accept an xyz fraction of error on the comparison then the solution is straightforward, like

Match = function (x,y, relative.tol)
{
 if (y<((1+relative.tol)*x))
  if (y>((1-relative.tol)*x))
    return(T)
 return(F)
}

Match(6, 6.001, 0.01)


Ugly as hell :vomit:, and will not work well if you get into extreme binary representations.

I could be wrong, but...

Best regards,
ElMaestro

R's base package has 274 reserved words and operators, along with 1761 functions. I can use 18 of them (about 14 of them properly). I believe this makes me the Donald Trump of programming.

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