qqplot

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qqplot

Vincent Negre
Hello,
I would like to use qqplot() to compare two
experimental distributions. But I do not understand
how qqplot() compute quantiles. In fact, quantile() do
not return the same results.
Thank you for your help.
Vincent.

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Re: qqplot

Duncan Murdoch
On 2/6/2006 9:59 AM, Vincent Negre wrote:
> Hello,
> I would like to use qqplot() to compare two
> experimental distributions. But I do not understand
> how qqplot() compute quantiles. In fact, quantile() do
> not return the same results.

Take a look at the source code.  qqplot replaces the longer vector with
one calculated by linear interpolation (that's what approx does) between
the values of the other.

Duncan Murdoch

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Re: qqplot

François Pinard
In reply to this post by Vincent Negre
[Vincent Negre]

>[...] I do not understand how qqplot() compute quantiles.

Just type ``qqplot`` (without the parentheses) at the R prompt, to see
the source code.  ``qqplot`` does not especially compute quantiles,
which are rather obtained directly through sorting its arguments.

--
François Pinard   http://pinard.progiciels-bpi.ca

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