how the break is calculated by R?

As to hist,the help file says:" R's default with equi-spaced breaks 
(also the default) is to plot the counts in the cells defined by 

breaks."

I wanna know how the break is calculated by R? 

In other words: break = (max - min)/(number of group) but how the 
"number of group" is calculated by R? Thanks!

If you look closely at the help page for hist, you'll see that in the 
Usage section it says breaks="Sturges".  Then in the Arguments section it 
says that when breaks is a character string, it means it is the name of a 
method to compute the number of cells.  Finally, in the Details section, 
it tells you to look at the nclass.Sturges help page for details of 
Sturges' algorithm.

Wikipedia has a good description of common alorgithms for calculating the 
number of breaks.
http://en.wikipedia.org/wiki/Histogram#Number_of_bins_and_width

Regards,
Richie.

Mathematical Sciences Unit
HSL


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