From martin.becker at mx.uni-saarland.de  Fri Apr  9 10:36:45 2010
From: martin.becker at mx.uni-saarland.de (Martin Becker)
Date: Fri, 09 Apr 2010 10:36:45 +0200
Subject: [Rd] hist.default()$density
In-Reply-To: <4BB21610.90407@mx.uni-saarland.de>
References: <4BB21610.90407@mx.uni-saarland.de>
Message-ID: <4BBEE71D.1000500@mx.uni-saarland.de>

Dear developers,

since running 'example(hist)' produces
...
hist> sum(r$density * diff(r$breaks)) # == 1
[1] 0.9999999
...
I suppose that the current behaviour of hist() is not as intended (and 
documented).
So, please find attached (and inline below) a (trivial) patch for 
hist.default().

Best wishes
  Martin


Index: src/library/graphics/R/hist.R
===================================================================
--- src/library/graphics/R/hist.R    (revision 51652)
+++ src/library/graphics/R/hist.R    (working copy)
@@ -111,7 +111,7 @@
     stop("negative 'counts'. Internal Error in C-code for \"bincount\"")
     if (sum(counts) < n)
     stop("some 'x' not counted; maybe 'breaks' do not span range of 'x'")
-    dens <- counts/(n*h)
+    dens <- counts/(n*diff(breaks))
     mids <- 0.5 * (breaks[-1L] + breaks[-nB])
     r <- structure(list(breaks = breaks, counts = counts,
             intensities = dens,



Martin Becker wrote:
> Dear developers,
>
> the current implementation of hist.default() calculates 'density' (and 
> 'intensities') as
>  dens <- counts/(n*h)
> where h has been calculated before as
>  h <- diff(fuzzybreaks)
> which results in 'fuzzy' values for the density, see e.g.
>
> > tmp <- hist(1:10,breaks=c(-2.5,2.5,7.5,12.5),plot=FALSE)
> > print(tmp$density,digits=15)
> [1] 0.0399999920000016 0.1000000000000000 0.0600000000000000
>
> Since hist.default()$breaks are not the fuzzy breaks used for the 
> calculation of dens, the sum of the bins' area is significantly 
> different from 1 in many cases, see e.g.
>
> > print(sum(tmp$density*diff(tmp$breaks)),digits=15)
> [1] 0.999999960000008
>
> Is this intended, or should the calculation of dens read
>  dens <- counts/(n*diff(breaks))
> instead (or should hist.default()$breaks return the fuzzy breaks)?
>
> Best wishes
>   Martin
>
>


-- 
Dr. Martin Becker
Statistics and Econometrics
Saarland University
Campus C3 1, Room 217
66123 Saarbruecken
Germany

-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: hist.diff
URL: <https://stat.ethz.ch/pipermail/r-devel/attachments/20100409/d0c95a61/attachment.pl>


[Rd] hist.default()$density
Martin Becker