[R] probability histogram question
Alec Stephenson
astephen at efs.mq.edu.au
Fri Aug 20 02:14:28 CEST 2004
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
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