[R] Histograms and Sturges rule

[Paul Smith]

On Nov 28, 2007 12:32 AM, Deepayan Sarkar <deepayan.sarkar at gmail.com> wrote:
> > According to the Sturges rule, the number of classes of a histogram is
> > the closest integer to
> >
> > 1 + logb(n,base=2)
> >
> > where n is the number of observations. The function hist(), by
> > default, uses the Sturges rule. However, the code
> >
> > x <- 1:200
> > hist(x)
> >
> > produces a histogram with 10 classes and not 9 classes as determined
> > by the Sturges rule. What am I missing?
>
> The documentation does say that:
>
>  In the last three cases the number is a suggestion only.
>
> Basically, hist() uses "pretty" breakpoints, and you have
>
> > pretty(c(1, 200),  9)
>  [1]   0  20  40  60  80 100 120 140 160 180 200
>
> (i.e. 10 intervals even when you ask for 9). truehist() in MASS and
> histogram() in lattice don't have this "feature" (though truehist
> doesn't seem to allow "Sturges" as an option).

Thanks, Deepayan, for the clarification.

Paul