hi!
there is a bug with the IF operator that is really dangerous!
please try the code below and if someone could explain to me why when (q is
equal to 0.8, 0.9 or 1) R do not print it?
q=0
for (j in 1:11){
if ((q==1)){
print(q)
}
q=q+0.1
}
so in this code q is incremented from 0 to 1.1. but R do not capture print
the value 1, 0.8 and 0.9 !! try to change (q==0.4) it gonna print 0.4. but
if you put q==0.8 or 0.9 or 1 it doesn't work!!!
please try it it is amazing!!!
--
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On 4/18/2011 9:12 AM, salmajj wrote:> hi! > there is a bug with the IF operator that is really dangerous! > please try the code below and if someone could explain to me why when (q is > equal to 0.8, 0.9 or 1) R do not print it? > > q=0 > for (j in 1:11){ > > if ((q==1)){ > print(q) > } > q=q+0.1 > } > > so in this code q is incremented from 0 to 1.1. but R do not capture print > the value 1, 0.8 and 0.9 !! try to change (q==0.4) it gonna print 0.4. but > if you put q==0.8 or 0.9 or 1 it doesn't work!!! > please try it it is amazing!!!It is not a bug. It a misunderstanding on your part of the limits of floating point arithmetic. See FAQ 7.31 (and multiple previous discussions on this and the r-help list). http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f> -- > View this message in context: http://r.789695.n4.nabble.com/Dangerous-Bug-with-IF-function-of-R-tp3457976p3457976.html > Sent from the R devel mailing list archive at Nabble.com. >-- Brian S. Diggs, PhD Senior Research Associate, Department of Surgery Oregon Health & Science University
On Mon, Apr 18, 2011 at 09:12:41AM -0700, salmajj wrote:> hi! > there is a bug with the IF operator that is really dangerous! > please try the code below and if someone could explain to me why when (q is > equal to 0.8, 0.9 or 1) R do not print it? > > q=0 > for (j in 1:11){ > > if ((q==1)){ > print(q) > } > q=q+0.1 > } > > so in this code q is incremented from 0 to 1.1. but R do not capture print > the value 1, 0.8 and 0.9 !! try to change (q==0.4) it gonna print 0.4. but > if you put q==0.8 or 0.9 or 1 it doesn't work!!! > please try it it is amazing!!!Incrementing a number by 0.1 produces numbers, which are not exactly representable in binary, so this operation involves a rounding error. Try the following q=0 for (j in 1:11){ if ((q==1)){ print(q) } q=round(q+0.1, digits=7) } Petr Savicky.
Thanks a lot Petr it works!!! You know for someone who is used to work with matlab it is not so obvious:) -- View this message in context: http://r.789695.n4.nabble.com/Dangerous-Bug-with-IF-function-of-R-tp3457976p3458300.html Sent from the R devel mailing list archive at Nabble.com.