[R] How is the relation between Frequency and Counts in hist/density defined?

[Bert Gunter]

Check the Help archives, google, search cran, as this has been
requested many times. IIRC, Greg Snow's gtools package has a function
that does this.

-- Bert

On Mon, May 23, 2011 at 8:39 AM, Tal Galili <tal.galili at gmail.com> wrote:
> Thanks Bery and Richard.
> So how would you suggest to create a histogram function with an added
> density plot on top of it?
> Here is what I've came up so far (ANY suggestion for improvement will be
> welcomed!):
>
> #-------------------------------------------------------------
> # function
> hist.plus.density <- function(X,..., density_col = "blue", density_lwd = 5,
> main)
> {
> if(missing(main))
> {
> xname <- paste(deparse(substitute(X), 500), collapse = "\n")
> main <- paste("Histogram of", xname)
> }
> a <- hist(X, main  = main , ...)
> y <- density(X)$y  * max(a$counts / a$density, na.rm = T)
> x <- density(X)$x
> lines(x = x, y = y, col = density_col, lwd = density_lwd)
> return(invisible(a))
> }
>
> # example of use:
>  set.seed(242)
>  z = rnorm(30)
>  hist.plus.density(z)
> #-------------------------------------------------------------
>
>
> Thanks,
> Tal
>
>
> ----------------Contact
> Details:-------------------------------------------------------
> Contact me: Tal.Galili at gmail.com |  972-52-7275845
> Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) |
> www.r-statistics.com (English)
> ----------------------------------------------------------------------------------------------
>
>
>
>
> On Mon, May 23, 2011 at 6:16 PM, Bert Gunter <gunter.berton at gene.com> wrote:
>>
>> ... Which makes the cumulative (discrete) distribution 1, as it should be.
>>
>> -- Bert
>>
>> On Mon, May 23, 2011 at 7:59 AM, Tal Galili <tal.galili at gmail.com> wrote:
>> > Thanks Richard!
>> >
>> > ----------------Contact
>> > Details:-------------------------------------------------------
>> > Contact me: Tal.Galili at gmail.com |  972-52-7275845
>> > Read me: www.talgalili.com (Hebrew) | www.biostatistics.co.il (Hebrew) |
>> > www.r-statistics.com (English)
>> >
>> > ----------------------------------------------------------------------------------------------
>> >
>> >
>> >
>> >
>> > On Mon, May 23, 2011 at 5:56 PM, <Richard.Cotton at hsl.gov.uk> wrote:
>> >
>> >>
>> >> > In order to do this I can use the relation between count and density,
>> >> > but
>> >> I
>> >> > would like to know if there is a way for me to predict it upfront.
>> >>
>> >> In the code for hist.default, you'll see the line
>> >>
>> >> dens <- counts/(n * diff(breaks))
>> >>
>> >> > Here is an example:
>> >> >
>> >> > set.seed(242)
>> >> > z = rnorm(30)
>> >> > hist_z <- hist(z)
>> >> > hist_z$counts / hist_z$density # the relation is 15
>> >>
>> >> In your example, n is 30, and the breaks are evenly spaced every 0.5.
>> >>
>> >> Regards,
>> >> Richie.
>> >>
>> >> Mathematical Sciences Unit*
>> >> **HSL* <http://www.hsl.gov.uk/contact-us.htm>*
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>>
>>
>> --
>> "Men by nature long to get on to the ultimate truths, and will often
>> be impatient with elementary studies or fight shy of them. If it were
>> possible to reach the ultimate truths without the elementary studies
>> usually prefixed to them, these would not be preparatory studies but
>> superfluous diversions."
>>
>> -- Maimonides (1135-1204)
>>
>> Bert Gunter
>> Genentech Nonclinical Biostatistics
>
>



-- 
"Men by nature long to get on to the ultimate truths, and will often
be impatient with elementary studies or fight shy of them. If it were
possible to reach the ultimate truths without the elementary studies
usually prefixed to them, these would not be preparatory studies but
superfluous diversions."

-- Maimonides (1135-1204)

Bert Gunter
Genentech Nonclinical Biostatistics