Dear CFers,
About a year ago I proposed three new cell-methods (mibs/mabs/mebs).
The proposal received some discussion, and what I infer from silence
as acquiescence. To those three methods I now propose adding a fourth:
tabs = total absolute value whose CF mehod would be encoded as
sum_absolute_value (or, if people prefer, total_absolute_value).
tabs is analogous to the existing "sum" statistic but is computed with
absolute values. Its utility is in computing statistics of quantities
whose magnitude not signedness is the key metric. Its omission in my
original proposal was an oversight.
The full set of recommendations could be implemented in CF by
inserting the following line into Table E.1. Cell Methods
http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/build/cf-conventions.html#appendix-cell-methods
cell_methods: Units: Description
maximum_absolute_value u Maximum absolute value
minimum_absolute_value u Minimum absolute value
mean_absolute_value u Mean absolute value
sum_absolute_value u The data values are representative of
a sum or accumulation of the absolute values over the cell.
Thoughts?
Best,
Charlie
On 2/20/15 00:55, David Hassell wrote:
> Hi Charlie,
>
>> the strings "maximum_absolute_value", "minimum_absolute_value",
>> and "mean_absolute_value". I suggest CF adopt this, or some
>> variant pursuant to discussion.
>
> Many apologies - for some reason, I failed to register this crucial
> sentence when I replied. I suppose that it's good that the same names
> were arrived at without prior knowledge.
>
> No objections from me, then.
>
> All the best,
>
> David
>
> ---- Original message from Charlie Zender (04PM 19 Feb 15)
>
>> Date: Thu, 19 Feb 2015 16:39:15 -0800
>> From: Charlie Zender <zender at uci.edu>
>> To: David Hassell <d.c.hassell at reading.ac.uk>
>> CC: CF Metadata Mail List <cf-metadata at cgd.ucar.edu>
>> Subject: Re: [CF-metadata] New cell_methods: mabs/mibs/mebs?
>> User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101
>> Thunderbird/31.4.0
>>
>> Hello David,
>>
>> I use mabs/mebs/mibs as shorthand, not as cell_methods.
>> I suggest, and NCO implements, cell_methods with the longer
>> versions that you prefer. The command line operators of NCO
>> accept either full or abbreviated versions (to save typing
>> when conducting the operation itself).
>>
>> Now I see what you mean by the sentence in the appendix.
>> It could be read either way, and I read it the wrong way.
>> So I like your suggestion to clarify it.
>>
>> Charlie
>>
>> On 02/19/2015 04:27 PM, David Hassell wrote:
>>> Dear Charlie,
>>>
>>> I for one have no objection, in general, to new cell methods - I don't
>>> think that there are enough.
>>>
>>> Your suggestions (mabs/mibs/mebs) are clearly well defined, though I'm
>>> personally not so keen on the use of abbreviations. I've not seen
>>> these terms before, and wouldn't have guessed what they all mean. This
>>> is contrary to all of the other cell methods, which are unabbreviated
>>> and, I suspect, nearly universally understood.
>>>
>>> I dislike typing as much as anyone, but spelling them out is only 1 to
>>> 4 characters more than typing standard_deviation, the current longest
>>> method name:
>>>
>>> standard_deviation
>>> mean_absolute_value
>>> minimum_absolute_value
>>> maximum_absolute_value
>>>
>>> These terms seem nicely self describing to me. Do you think this is an
>>> option?
>>>
>>>> There appears to be an error in the draft 1.7 document. The sentence
>>>> describing Appendix E (the cell-methods appendix) says "In the Units
>>>> column, u indicates the units of the physical quantity before the
>>>> method is applied." Actually the units column entries are valid
>>>> _after_ the method is applied. Variance is the only method for which
>>>> this currently matters. This can be addressed independently of the
>>>> rest of the cell_methods suggestions proposed here.
>>>
>>> I think that this is OK. The column contains units after the method is
>>> applied, defined in terms of the original units ('u'). However, I
>>> agree that the terse description can mislead (as it did me just
>>> now!). How about replacing:
>>>
>>> "In the Units column, 'u' indicates the units of the physical
>>> quantity before the method is applied."
>>>
>>> with something like:
>>>
>>> "The Units column contains the units of the physical quantity after
>>> the method is applied, in terms of 'u', the units before the method
>>> is applied."
>>>
>>>
>>> All the best,
>>>
>>> David
>>>
>>>
>>> ---- Original message from Charlie Zender (11AM 19 Feb 15)
>>>
>>>> Date: Thu, 19 Feb 2015 11:56:22 -0800
>>>> From: Charlie Zender <zender at uci.edu>
>>>> To: CF Metadata Mail List <cf-metadata at cgd.ucar.edu>
>>>> Subject: [CF-metadata] New cell_methods: mabs/mibs/mebs?
>>>> User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0)
>>>> Gecko/20100101 Thunderbird/31.4.0
>>>>
>>>> Dear CF-ers,
>>>>
>>>> The statistics mabs/mibs/mebs stand for "Maximum absolute value",
>>>> "Minimum absolute value", and "Mean absolute value", respectively.
>>>> They are similar to max/min/mean statistics, and they can be useful
>>>> in characterizing data when one wants positive-definite metrics.
>>>> mebs (unlike mean) does not allow positive and negative values to
>>>> compensate eachother. Unlike rms, mebs not does weight outliers
>>>> quadratically. NCO (version 4.4.8) implements mabs/mibs/mebs as
>>>> fundamental statistics (like max/min/mean/rms), and annotates the
>>>> cell_methods attribute of variables reduced by these statistics with
>>>> the strings "maximum_absolute_value", "minimum_absolute_value", and
>>>> "mean_absolute_value". I suggest CF adopt this, or some variant
>>>> pursuant to discussion.
>>>>
>>>> So I guess this is a request for discussion.
>>>> The relevant portions of CF are
>>>> http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/build/cf-conventions.html#cell-methods
>>>> http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/build/cf-conventions.html#appendix-cell-methods
>>>> The modifications that would be needed seem straightforward:
>>>> mention mabs/mebs/mibs in the text and then enlarge the existing
>>>> cell_methods table table by three rows.
>>>>
>>>> There appears to be an error in the draft 1.7 document. The sentence
>>>> describing Appendix E (the cell-methods appendix) says "In the Units
>>>> column, u indicates the units of the physical quantity before the
>>>> method is applied." Actually the units column entries are valid
>>>> _after_ the method is applied. Variance is the only method for which
>>>> this currently matters. This can be addressed independently
>>>> of the rest of the cell_methods suggestions proposed here.
>>>
>>> I think that this is OK. The column contains units after the method is
>>> applied, defined in terms of the original units ('u'). However, the
>>> terse description is misleading on first reading. How about something
>>> like:
>>>
>>> "In the Units column are the units of the physical quantity after the
>>> method is applied, in terms of 'u', the units before the method is
>>> applied."
>>>
>>>> Best,
>>>> Charlie
>>>> --
>>>> Charlie Zender, Earth System Sci. & Computer Sci.
>>>> University of California, Irvine 949-891-2429 )'(
>>>> _______________________________________________
>>>> CF-metadata mailing list
>>>> CF-metadata at cgd.ucar.edu
>>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>>
>>>
>>> --
>>> David Hassell
>>> National Centre for Atmospheric Science (NCAS)
>>> Department of Meteorology, University of Reading,
>>> Earley Gate, PO Box 243,
>>> Reading RG6 6BB, U.K.
>>>
>>> Tel : +44 118 3785613
>>> E-mail: d.c.hassell at reading.ac.uk
>>>
>>
>> --
>> Charlie Zender, Earth System Sci. & Computer Sci.
>> University of California, Irvine 949-891-2429 )'(
>
>
> --
> David Hassell
> National Centre for Atmospheric Science (NCAS)
> Department of Meteorology, University of Reading,
> Earley Gate, PO Box 243,
> Reading RG6 6BB, U.K.
>
> Tel : +44 118 3785613
> E-mail: d.c.hassell at reading.ac.uk
>
--
Charlie Zender, Earth System Sci. & Computer Sci.
University of California, Irvine 949-891-2429 )'(
Received on Tue Feb 16 2016 - 17:05:57 GMT
