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*Subject*: Re: median function*From*: Dick Jackson <djackson(at)dfanning.com>*Date*: Thu, 22 Jul 1999 15:19:25 GMT*Newsgroups*: comp.lang.idl-pvwave*Organization*: Fanning Software Consulting*References*: <37965009.EEFBE62D@ssl.berkeley.edu>*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:15782

Hi Harald, Harald Frey wrote: > > I see a problem in the median function and would like to get your > general opinion. > > 1. The median function has no /Nan option like total or mean. I think you will be happy to know that the newly-released IDL 5.2.1 (see www.rsinc.com for your update!) has the following release note: MEDIAN Function Improvement: ---------------------------- The MEDIAN function now treats NaN values as missing data. > IDL> a=findgen(9) > IDL> print,total(a),mean(a),median(a) > 36.0000 4.00000 4.00000 > IDL> a[0]=!values.f_nan > IDL> print,total(a),mean(a),median(a) > NaN NaN 4.00000 > % Program caused arithmetic error: Floating illegal operand That was in 5.2, but now in 5.2.1, after the same instructions: IDL> print,total(a),mean(a),median(a) NaN NaN 5.00000 > 2. The Nan values are not properly handled in the determination of the > median. In the first case the Nan values are interpreted as 0. and in > the second case as very large. > > IDL> a=findgen(9) > IDL> a[0]=!values.f_nan > [...] > IDL> a[1]=!values.f_nan > IDL> print,a > NaN NaN 2.00000 3.00000 4.00000 > 5.00000 > 6.00000 7.00000 8.00000 > IDL> print,median(a) > 6.00000 > % Program caused arithmetic error: Floating illegal operand Again, with the new 5.2.1: IDL> print,median(a) 5.00000 I think you will find this satisfactory! Cheers, -- -Dick Dick Jackson Fanning Software Consulting, Canadian Office djackson@dfanning.com Calgary, Alberta Voice/Fax: (403) 242-7398 Coyote's Guide to IDL Programming: http://www.dfanning.com/

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