I think the reason why functions for calculating quartiles (or more generally,
percentiles) are not in many software packages is because they can be
computationally expensive to compute.
The only way I know how to generate percentiles is to first sort the data into
numeric order, and then select the appropriate value from the list. Sorting is
expensive, especially when there are a lot of data. Is there a better/faster
way of computing percentiles?
Tim Hume
Centre for Australian Weather and Climate Research
Melbourne
Australia
-----Original Message-----
From: Gerry Creager [mailto:gerry.creager@xxxxxxxx]
Sent: Monday, 12 May 2008 12:41
To: Timothy Hume
Cc: Dennis Shea
Subject: Re: [netcdfgroup] Calculating medians, quartiles etc of a variable in
a NetCDF file.
I'd consider looking at the NCAR command language and seeing if quartile
calculation is native therein. I'd be surprised if it's not, or easily
computable, but I did not find it initially.
Check http://www.ncl.ucar.edu/ and consider joining the mailing list
long enough to find out.
Timothy Hume wrote:
> Hi,
>
> I have an application where I would like to calculate quartiles of a variable
> in a NetCDF file (I am computing the trimean: TM = 0.25*(Q1 + 2Q2 + Q3) )
>
> The NetCDF operators are excellent for computing arithmetic means, but don't
> include the capability to compute quartiles. Before I start writing my own
> code to compute quartiles, does anyone know of some software which already
> does this? Basically, I am looking for the equivalent of ncwa with a quartile
> operation.
>
> Thanks,
>
> Tim Hume
> Centre for Australian Weather and Climate Research
> Melbourne
> Australia
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--
Gerry Creager -- gerry.creager@xxxxxxxx
Texas Mesonet -- AATLT, Texas A&M University
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