[R] probability histogram question
Joseph LeBouton
lebouton at msu.edu
Fri Aug 20 02:28:47 CEST 2004
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
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