Message-ID: <8BD65841-FA65-4504-8B45-C6537E5706A1@gmail.com>
Date: 2012-01-14T16:40:09Z
From: Peter Dalgaard
Subject: Quantiles in boxplot
In-Reply-To: <SNT128-W62A0AA94C886813F13025A899D0@phx.gbl>
On Jan 14, 2012, at 16:07 , Ren? Brinkhuis wrote:
>
> Based
> on your information I created a custom function for calculating the
> first and third quartile according to the 'boxplot logic'.
A more compact (though not as readable) version is afforded by stats:::fivenum.
A convenient description is (I believe) that the hinges are the medians of the bottom and top halves of the sorted observations, with the middle observation counting in both groups if n is odd).
> x <- rnorm(121)
> fivenum(x)
[1] -2.4596038 -0.6034689 0.1105829 0.6686026 2.2580863
> median(sort(x)[1:floor((length(x)+1)/2)])
[1] -0.6034689
> median(sort(x)[ceiling((length(x)+1)/2):length(x)])
[1] 0.6686026
--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk Priv: PDalgd at gmail.com