From martin.becker at mx.uni-saarland.de  Tue Mar 30 17:17:36 2010
From: martin.becker at mx.uni-saarland.de (Martin Becker)
Date: Tue, 30 Mar 2010 17:17:36 +0200
Subject: [Rd] hist.default()$density
Message-ID: <4BB21610.90407@mx.uni-saarland.de>

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 206
66123 Saarbruecken
Germany



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