histogram first bar wrong position

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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