Re: [R] hist densities

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Fri, 21 Mar 2008 15:28:58 +0000 (GMT)

On Fri, 21 Mar 2008, Luke Spadavecchia wrote:

> Hi there,
>
> I was wondering why
>
> x<-rnorm(n=5000,mean=1.5,sd=0.25)
> h<-hist(x)
> sum(h$density)
>
> [1] 10
>
> I thought the integral of the histogram should be one? These seems
> strange to me, or am I being silly...

The integral is not a sum of heights but of areas. You need sum(h$density * diff(h$breaks)), and this is spelled out on the help page.

> Regards Luke Spadavecchia
>
> PS. I'm using R 2.5.1 on Mac OSX

-- 
Brian D. Ripley,                  ripley_at_stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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Received on Fri 21 Mar 2008 - 15:31:39 GMT

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