Re: [R] Calculating Percentile in R

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Mon, 18 Jun 2007 08:12:21 +0100 (BST)

On Sun, 17 Jun 2007, Megh Dal wrote:

> Hi all,
>
> I have a problem on how R calculates Percentiles :
>
> Suppose I have following data set:
>> data1
> [1] -16648185 -14463457 -14449400 -13905309 -13443436 -13234755 -12956282 -11660896
> [9] -10061040 -9805005 -9789583 -9754642 -9562164 -9391709 -9212182 -9151073
> [17] -9092732 -9068214 -8978151 -8943912 -8761890 -8632106 -8541580 -8501249
> [25] -8234466 -8219015 -8193543 -7488279 -7340768 -7236684 -7225458 -7159465
> [33] -6819625 -6810858 -6755620 -6626439 -6610901 -6551762 -6207377 -6192583
> [41] -6106783 -6077051 -6035300 -6035195 -6019017 -5954375 -5946285 -5886082
> [49] -5880402 -5723368 -5668698 -5599168 -5548276 -5445734 -5412312 -5384707
> [57] -5309365 -5303425 -5285274 -5204585 -5096301 -5092182 -5053349 -5041533
> [65] -5021234 -5005402 -4984232 -4981990 -4964457 -4936653 -4920384 -4918021
> [73] -4895351 -4843258 -4824730 -4774792 -4771018 -4616156 -4590430 -4444262
> [81] -4443954 -4435397 -4415112 -4374465 -4341858 -4267891 -4252410 -4185021
> [89] -4164458 -4158863 -4020436 -4006030 -3975819 -3959667 -3916414 -3876878
> [97] -3765340 -3729338 -3713670 -3634991
>
> Now the 5th percentile should be value corresponding to 0.05*(100+1) =
> 5.05 = 5 (rounded)

According to you, but not according to ?quantile, which gives you a choice of 9 definitions, yours not being the default.

> hence : -13443436
>
> But R give the value :
>> quantile(data1, 0.05)
> 5%
> -13245189
>
> Can anyone clarify me on this regards?
>
> Thanks
> Megh
>
>
> [[alternative HTML version deleted]]
>
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html

PLEASE do as we ask.

-- 
Brian D. Ripley,                  ripley_at_stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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Received on Mon 18 Jun 2007 - 07:19:29 GMT

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