R devel - Jun 2004 - a fault in the "hist" - function (PR#6931)

Full_Name: Stephan Schlueter
Version: 1.9.0
OS: 
Submission from: (NULL) (217.184.109.24)


During my studies, I found a fault in the hist()-function:
If you have a vector x with values around zero and also bigger than 10,000,000 ,
there will be a shift of   -max(x)/10,000,000    in the hist-datas.
See my example:

x<-runif(10000)
hist(x,breaks=c(seq(-3,3,0.1)),prob=TRUE)
#everything ok, but now produce the problem 
x[254]=20000000
hist(x,breaks=c(seq(-3,3,0.1),max(x)),prob=TRUE,xlim=c(-3,3))
#here you can see the shift

hist(x + max(x)/10000000,breaks=c(seq(-3,3,0.1),max(x)),prob=TRUE,xlim=c(-3,3))
#first solution (but I don't know ,why it works)

for(i in 1:10000)
 {
 if(x[i]>10)x[i]=10
 }
hist(x,breaks=c(seq(-3,3,0.1),max(x)),prob=TRUE,xlim=c(-3,3))
#second solution (the better one I think)


Good Luck for the solution of this problem, and it would be nice to send me an
answer. 
               Thanks and till then,  Stephan Schlueter

stephanschlueter@gmx.de wrote:
> Full_Name: Stephan Schlueter
> Version: 1.9.0
> OS: 
> Submission from: (NULL) (217.184.109.24)
> 
> 
> During my studies, I found a fault in the hist()-function:
> If you have a vector x with values around zero and also bigger than
10,000,000 ,
> there will be a shift of   -max(x)/10,000,000    in the hist-datas.
> See my example:
> 
> x<-runif(10000)
> hist(x,breaks=c(seq(-3,3,0.1)),prob=TRUE)
> #everything ok, but now produce the problem 
> x[254]=20000000
> hist(x,breaks=c(seq(-3,3,0.1),max(x)),prob=TRUE,xlim=c(-3,3))
> #here you can see the shift
> 
> hist(x +
max(x)/10000000,breaks=c(seq(-3,3,0.1),max(x)),prob=TRUE,xlim=c(-3,3))
> #first solution (but I don't know ,why it works)
> 
> for(i in 1:10000)
>  {
>  if(x[i]>10)x[i]=10
>  }
> hist(x,breaks=c(seq(-3,3,0.1),max(x)),prob=TRUE,xlim=c(-3,3))
> #second solution (the better one I think)
> 
> 
> Good Luck for the solution of this problem, and it would be nice to send me
an
> answer. 
>                Thanks and till then,  Stephan Schlueter
> 
> ______________________________________________
> R-devel@stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-devel

The problem is in hist.default():

     diddle <- 1e-7 * max(abs(range(breaks)))

and whereever we are diddling - there are some disadvantages.

Do we want a flag that turns off diddling and the following "fuzz" 
stuff? Or do we want something to adjust the hardcoded heuristical value 
"1e-7" (to zero, for example)?

Uwe Ligges

On 2 Jun 2004, Peter Dalgaard wrote:
> ligges@statistik.uni-dortmund.de writes:
> 
> > The problem is in hist.default():
> > 
> >      diddle <- 1e-7 * max(abs(range(breaks)))
> > 
> > and whereever we are diddling - there are some disadvantages.
> > 
> > Do we want a flag that turns off diddling and the following
"fuzz"
> > stuff? Or do we want something to adjust the hardcoded heuristical
value
> > "1e-7" (to zero, for example)?
> 
> Neither, I think, since the diddle is there for a reason, and the only
> real problem is the use of breaks that are wildly off-scale. We might
> key diddle to xlim instead, or possibly let "diddle" be an
argument
We can't do that, as hist might not be used to plot.
> with a suitable default. 
> 
> You probably can't get all cases completely right though. A tiny range
> of numbers (compared to the mean) is likely to cause problems whatever
> you do.
I think the fuzz really needs to be relative to the adjacent bin size (and 
the one to the left or right as appropriate).  So I am going to replace

    diddle <- 1e-7 * max(abs(range(breaks)))

by

    diddle <- 1e-7 * median(diff(breaks))

that is to use a typical bin size to set the fuzz factor.  (Note: I know
this is typically a bit smaller, but 1e-7 was a rather large tolerance.)

[I hadn't realized we used the largest limit and not the range (normal 
sense) of the data.  There is also something of a design error in that we 
shift the breaks and not the data.]

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595