[GRASS-dev] Re: [GRASS GIS] #474: r.quantile: segfaults with percentile=100

[Moritz Lennert]

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