[R] histogram first bar wrong position
William Dunlap
wdunlap at tibco.com
Thu Dec 22 17:36:34 CET 2016
Looking at the return value of hist will show you what is happening:
> x <- rep(1:6,10*(6:1))
> z <- hist(x, freq=TRUE)
> z
$breaks
[1] 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
$counts
[1] 60 50 0 40 0 30 0 20 0 10
...
The the first bin is [1-1.5], including both endpoints, while the other
bins include only the upper endpoint. I recommend defining your
own breakpoints, ones don't include possible data points, as in
> print(hist(x, breaks=seq(min(x)-0.5, max(x)+0.5, by=1), freq=TRUE))
$breaks
[1] 0.5 1.5 2.5 3.5 4.5 5.5 6.5
$counts
[1] 60 50 40 30 20 10
...
S+ had a 'factor' method for hist() that did this sort of thing, but R does
not.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Thu, Dec 22, 2016 at 5:17 AM, itpro <itpro1 at yandex.ru> wrote:
> Hi, everyone.
>
>
> I stumbled upon weird histogram behaviour.
>
> Consider this "dice emulator":
> Step 1: Generate uniform random array x of size N.
> Step 2: Multiply each item by six and round to next bigger integer to get
> numbers 1 to 6.
> Step 3: Plot histogram.
>
> > x<-runif(N)
> > y<-ceiling(x*6)
> > hist(y,freq=TRUE, col='orange')
>
>
> Now what I get with N=100000
>
> > x<-runif(100000)
> > y<-ceiling(x*6)
> > hist(y,freq=TRUE, col='green')
>
> At first glance looks OK.
>
> Now try N=100
>
> > x<-runif(100)
> > y<-ceiling(x*6)
> > hist(y,freq=TRUE, col='red')
>
> Now first bar is not where it should be.
> Hmm. Look again to 100000 histogram... First bar is not where I want it,
> it's only less striking due to narrow bars.
>
> So, first bar is always in wrong position. How do I fix it to make
> perfectly spaced bars?
>
>
>
>
>
>
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