[R] identical values not so identical? newbie help please!

[Joshua Wiley]

On Thu, Mar 10, 2011 at 10:34 AM, maiya <maja.zaloznik at gmail.com> wrote:
> Thanks Josh and Dan!
>
> I did figure it had something to do with the machine epsilon...
>
> But so what do I do now? I'm calculating the total absolute error over
> thousands of tables e.g.:
> tae<-sum(abs(obs-exp))
> Is there any easy way to I keep these ignorable errors from showing up?

Well slight non zero values will not stop you from taking the sum of
the absolute errors (and presumably will not overly bias it).  Then
rather than report the total number of tae that equal 0 (you say about
10 out of what should be 60), report something like:

sum(abs(tae) < epsilon)

> And furthermore, why does this happen only sometimes? The two (2D) tables I
> attached are actually just one 'layer' in a 3D table. And only 2 out of
> about 400 layers had this happen, all the other ones are identical -
> perfectly! And out of 2000 3D tables, about 60 of which should have no
> error, only 10 actually show an error of zero, and in the rest this same
> thing happens in a few layers.
>
> OK, this is a bit messy for a real question. I mean I can just round down
> all the errors that are under 1e-8 or something, but I'd much rather this
> not happen in the first place?

I think we all would.  There is a whole vast literature and field on
this topic (far beyond my knowledge), that you can look into if you
think this will be a problem for your work (or just find the topic
fascinating).

> Thanks again to the two posters for bothering with me!

Your welcome.  Good luck finding a satisfying solution!

Josh

>
> Maja.
>
> --
> View this message in context: http://r.789695.n4.nabble.com/identical-values-not-so-identical-newbie-help-please-tp3346078p3346516.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/