Re: [R] Probabilities greather than 1 in HIST

From: Dennis Murphy <djmuser_at_gmail.com>
Date: Thu, 03 Mar 2011 10:20:20 -0800

Hi:

Here's an example:

x <- rnorm(300)
hist(x, breaks = 15, yaxt = 'n', ylab = 'Relative frequency') axis(2, at = seq(0, 50, by = 10), labels = round(seq(0, 50, by = 10)/length(x), 3))

HTH,
Dennis

On Thu, Mar 3, 2011 at 8:29 AM, jpmaroco <jpmaroco_at_gmail.com> wrote:

> Dear David,
>
> Thanks for your prompt reply.
>
> I see your point. But how can I get a histogram with relative frequencies?
> If I use
>
> >plot(xhist,yhist)
>
> I get absolute frequencies in the Y axis.

>
> Best,
>
> Joao
>
>
>
> From: David Winsemius [via R] [mailto:
> ml-node+3333619-1272092771-215234_at_n4.nabble.com]
> Sent: quinta-feira, 3 de Março de 2011 16:01
> To: jpmaroco
> Subject: Re: Probabilities greather than 1 in HIST
>
>
>
>
> On Mar 3, 2011, at 8:03 AM, jpmaroco wrote:
>
>
> > Dear all,
> > I am a newbie in R and could not find help on this problem. I am
> > trying to
> > plot an histogram with probabilities in the y axis. This is the code
> > I am
> > using:
> >
> > #TLC uniform
> > n=30
> > mi=1; mx=6
> > nrep=1000
> > xbar=rep(0,nrep)
> > for (i in 1:nrep) {xbar[i]=mean(runif(n,min=mi,max=mx))}
> > hist(xbar,prob=TRUE,breaks="Sturges",xlim=c(1,6),main=paste("n =",n),
> > xlab="Média", ylab="Probabilidade")
> > curve(dnorm(x,mean=mean(xbar),sd=sd(xbar)),add=TRUE,lwd=2,col="red")
> >
> > The problem is that I am getting greater than 1 probabilities in the
> > Y axis?
> > Is there a way to correct this?
>
>
> Despite the argument name, which I agree suggests that probabilities
> will be plotted, what is really described in the help page is that
> densities will be plotted, and densities may be greater than 1. You
> can suppress plotting of the y-axis, calculate the probabilities for
> each of the groups returned by hist, and then use the axes function.
>
> > xhist <- hist(xbar,breaks="Sturges",plot=FALSE)
> > yhist <- xhist$counts/sum(xhist$counts)
> > yhist
> [1] 0.002 0.027 0.087 0.236 0.287 0.228 0.107 0.021 0.004 0.001
>
>
>
>
> > Many thanks in advance.
> > Joao
> >
> > --
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>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
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