Why don't you specifically tell hist what breaks to use:

hist(x, breaks=seq(min(x), max(x), length=50), include.lowest=TRUE)

On Mon, May 19, 2008 at 5:31 AM, Ted Harding <Ted.Harding@manchester.ac.uk>
wrote:

> Hi Folks,
> I'd like to know how hist() decides how many cells to use
> when it ignores my "suggestion" to use say 'hist(...,breaks=50)'.
>
> More specifically, I have the results of 10000 simulations,
> each returning an 8-vector, therefore 8 variables each with
> 10000 values. Some of these 8 have somewhat skew distributions.
> Say one of these 8 variables is X.
>
> I ask for H <- hist(X,breaks=50), and get a histogram which
> usually has a different number of cells than what I intended.
>
> For instance, for one of these simulations, the 8 different
> values of length(H$breaks) are:
>
>  70, 44, 38, 68, 50, 40, 46, 45
>
> ?hist tells me
>
> A)
>  breaks: one of:
>    *  a vector giving the breakpoints between histogram
>       cells,
>    *  a single number giving the number of cells for the
>       histogram,
>    *  a character string naming an algorithm to compute the
>       number of cells (see Details),
>    *  a function to compute the number of cells.
>
>    In the last three cases the number is a suggestion only.
>
> B)
>  The default for 'breaks' is '"Sturges"': see 'nclass.Sturges'.
>
> If I look at the code for nclass.Sturges() I see
>
>  function (x) ceiling(log2(length(x)) + 1)
>
> and, for length(X) = 10000, this gives 15. This is not related
> to any of the numbers of breaks I actually got, in any way obvious
> to me.
>
> So:
> Question 1: hist() has apparently ignored my "suggestion" of
>  "break=50". Why? What is the criterion for ignoring?
>
> Question 2: Presumably, if it ignores the "suggestion", it
>  does something else, of its choice. I would then, perhaps,
>  expect it to fall back to its default, which is (allegedly)
>  Sturges. But the result from nclass.Sturges looks different
>  from what it actually did. So what did it actually do, and
>  how did it decide on this?
>
> With thanks,
> Ted.
>
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <Ted.Harding@manchester.ac.uk>
> Fax-to-email: +44 (0)870 094 0861
> Date: 19-May-08                                       Time: 10:31:20
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

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