[R] Inconsistency using seq

Hi all, Is there any problem of precision when using seq?. For example: x- seq(0,4,0.1) x[4]=0.3 BUT: x[4]-0.3=5.551115e-17 It means when I use this condition within an if clause, it does not find values with 0.3 for x[4] as it is not precisely 0.3. Is there any bug in seq() ? -- View this

Re: [R] Inconsistency using seq

Le lundi 18 juin 2012 à 12:58 -0700, hamoreno a écrit : Hi all, Is there any problem of precision when using seq?. For example: x- seq(0,4,0.1) x[4]=0.3 BUT: x[4]-0.3=5.551115e-17 It means when I use this condition within an if clause, it does not find values with 0.3 for x[4] as

Re: [R] Inconsistency using seq

Please read R FAQ 7.31. The problem is with your computer (and everyone else's), and has nothing to do with seq(). On Mon, Jun 18, 2012 at 3:58 PM, hamoreno hamor...@asu.edu wrote: Hi all, Is there any problem of precision when using seq?. For example: x- seq(0,4,0.1) x[4]=0.3 BUT:

Re: [R] Inconsistency using seq

No, this is rather the nature of floating point calculations. You may perhaps be looking for ?all.equal or R FAQ 7.31 (I think that's the one) which is google-able. It's a complicated subject, but those should get you started. Best, Michael On Jun 18, 2012, at 2:58 PM, hamoreno

Re: [R] Inconsistency using seq

Thanks everyone... Seems that I will have to use round before seq to make sure everything has the correct precision. -- View this message in context: http://r.789695.n4.nabble.com/Inconsistency-using-seq-tp4633739p4633750.html Sent from the R help mailing list archive at Nabble.com.

Re: [R] Inconsistency using seq

Nope. round() is not failsafe either. Basically, there is theoretically no way to guarantee immunity to floating point error in conditional comparisons. You need to either switch to integers -- which **are** exactly represented -- or figure out another way. Of course, practically speaking,

Re: [R] Inconsistency using seq

actually, you should build your sequences with integers and scale those to get floating point sequences. --- Jeff NewmillerThe . . Go Live... DCN:jdnew...@dcn.davis.ca.us

Re: [R] Inconsistency using seq

FYI, isZero - function(x, neps=1, eps=.Machine$double.eps, ...) { + (abs(x) neps * eps) + } x - seq(from=0, to=4, by=0.1) isZero(x[4]-0.3) [1] TRUE isZero(x[4]-0.3, neps=1) [1] TRUE isZero(x[4]-0.3, neps=0.1) [1] FALSE You could also have called isZero() isValueSmallEnoughForWhatINeed().

Re: [R] Inconsistency using seq

On Mon, Jun 18, 2012 at 12:58:13PM -0700, hamoreno wrote: Hi all, Is there any problem of precision when using seq?. For example: x- seq(0,4,0.1) x[4]=0.3 BUT: x[4]-0.3=5.551115e-17 It means when I use this condition within an if clause, it does not find values with 0.3 for x[4]