The explanation is in ?boxplot.stats (as the help for boxplot states).
Details:
The two ?hinges? are versions of the first and third quartile,
i.e., close to ?quantile(x, c(1,3)/4)?. The hinges equal the
quartiles for odd n (where ?n <- length(x)?) and differ for even
n. Whereas the quartiles only equal observations for ?n %% 4 = 1? (n =
1 mod 4), the hinges do so _additionally_ for ?n %% 4 = 2? (n = 2 mod 4),
and are in the middle of two observations
otherwise.
And so on, with references.
Sarah
2012/1/13 Ren? Brinkhuis <rene.brinkhuis at
live.nl>:>
> Hi,
>
> I have a simple question about quartiles in R, especially how they are
calculated using the boxplot.
> Quartiles
> ?(.25 and .75) in boxplot are different from the summary function and
> also don't match with the 9 types in the quantile function.
> See attachment for details.
> Can you give me the details on how the boxplot function does calculate
these values?
>
> Cheers,
> Rene Brinkhuis (Netherlands)
--
Sarah Goslee
http://www.functionaldiversity.org