[R] probability histogram question

[Joseph LeBouton]

Alec,

Thanks for your reply.  I guess what I'm getting at is that I to plot 
the histogram such that the HEIGHT of each bar represents the proportion 
of that class in the sample.  From your reply I gather that the AREA of 
each bar is currently representing the proportion.

My current work-around is to not plot the histogram immediately; I set 
it up (with plot=F), divide h$density by 10, then plot h;

x <- runif(100,0,1)
h <- hist(x, freq=F, plot=F)
h$density <- h$density/10
plot(h, freq=F)

while this is up to my normal hacking modus operandi, it's not terribly 
efficient.  Is there another way to do that?  Or is what I'm trying to 
do a perceptually and/or statistically incorrect way to think about 
histograms?

Thanks again,

jlb

Alec Stephenson wrote:

> 
> Alec Stephenson                                               
> Department of Statistics
> Macquarie University
> NSW 2109, Australia 
> 
> 
>>>>Joseph LeBouton <lebouton at msu.edu> 08/20/04 09:56am >>>
> 
> Hello, all;
> 
> I get an unexpected result when trying to plot a probability histogram
> with R1.9.1 on windows xp:
> 
> #with the following code:
> 
> 
>>x <- runif(100,0,1)
>>hist(x)
>>hist(x, freq=F)
>>h <- hist(x, freq=F)
>>summary(h)
> 
> 
> #            Length Class  Mode
> #breaks      11     -none- numeric
> #counts      10     -none- numeric
> #intensities 10     -none- numeric
> #density     10     -none- numeric
> #mids        10     -none- numeric
> #xname        1     -none- character
> #equidist     1     -none- logical
> 
> # The help file says that <h$density>  holds the values
> #	plotted in the probability histogram.  If that's the
> #	case, I'd expect that the sum of h$density for a histogram
> 	where freq=F would equal 1.0 ...  However:
> 
> 
>>sum(h$density)
> 
> 
> #returns the value :
> #[1] 10
> 
> I would really like to plot values in the probablility histogram that
> sum to 1, not 10.  Is there a switch in the hist(x) command that I'm
> missing?  Or, is there another function that can do this?
> 
> The width of each bar is 0.1, so you need
> sum(h$density) * 0.1
> or in general
> sum(h$density * diff(h$breaks))
> 
> Thanks,
> Alec
> 
> 
> 
> 

-- 
************************************
Joseph P. LeBouton
Forest Ecology PhD Candidate
Department of Forestry
Michigan State University
East Lansing, Michigan 48824

Office phone: 517-355-7744
email: lebouton at msu.edu