[GRASS-dev] Re: [GRASS GIS] #474: r.quantile: segfaults with
percentile=100
Moritz Lennert
mlennert at club.worldonline.be
Wed Feb 11 12:56:13 EST 2009
On 11/02/09 18:46, Dylan Beaudette wrote:
> On Wednesday 11 February 2009, GRASS GIS wrote:
>> #474: r.quantile: segfaults with percentile=100
>> ---------------------+-----------------------------------------------------
>> - Reporter: hamish | Owner: grass-dev at lists.osgeo.org
>> Type: defect | Status: closed
>> Priority: major | Milestone: 6.4.0
>> Component: Raster | Version: svn-develbranch6
>> Resolution: fixed | Keywords: r.quantile
>> Platform: Linux | Cpu: x86-32
>> ---------------------+-----------------------------------------------------
>> - Comment (by glynn):
>>
>> Replying to [comment:4 hamish]:
>> > I notice that if you do 'quant=3' you only get 2 results, and 'quant=1'
>>
>> gives no output. (all others do the same, report n-1)
>>
>> > Is this intended because 3 bins will have two separators (at 33% and
>>
>> 66%), or is it a bug?
>>
>> It's intended so that quant=N gives "N-tiles", e.g. quant=4 gives
>> quartiles, quant=10 gives deciles, etc. AIUI, the convention is not to
>> include the endpoints, e.g. "quartiles" are given as 25%, 50%, and 75%.
>
> Is this a convention? I am not a math/stats expert, but in R I see that the
> convetion is to report it like this:
>
> # generate some random data
> x <- rnorm(100)
> # compute quartiles:
> quantile(x)
> 0% 25% 50% 75% 100%
> -2.1691897 -0.3627331 0.1307290 0.6652009 2.4798260
>
> # we can see that it includes the min/max:
> summary(x)
> Min. 1st Qu. Median Mean 3rd Qu. Max.
> -2.16900 -0.36270 0.13070 0.07639 0.66520 2.48000
>
> Is this just a display/semantics thing?
Personally, I would prefer that min and max are also shown (like the
output with the -r flag). Otherwise you have to look for those values
somewhere else, and I do find it useful to have them.
Moritz
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