[ncl-talk] Add new options for dim_cumsum

[Dave Allured - NOAA Affiliate]

Dennis,

> I tagged this for the 6.5.0 release but that may not be possible.

No problem.  Please put this into the pile for "would be nice to have some
day".  Thanks.

--Dave


On Mon, Nov 27, 2017 at 8:11 AM, Dennis Shea <shea at ucar.edu> wrote:

> Dave,
>
> A ticket has been opened:  JIRA-2699: dim_cumsum_n: add new options
>
> -------------
> I tagged this for the 6.5.0 release but that may not be possible.
>
> Regards
>
> On Fri, Nov 24, 2017 at 2:38 PM, Dave Allured - NOAA Affiliate <
> dave.allured at noaa.gov> wrote:
>
>> NCL team,
>>
>> I would like to suggest several new options for the dim_cumsum family of
>> four functions.  The current three options are:
>>
>> opt = 0 ; when _FillValue is encountered no additional summing will be
>> performed.
>> opt = 1 ; when _FillValue is encountered set element to _FillValue and
>> resume summing.
>> opt = 2 ; treat _FillValue as numeric zero when summing.
>>
>> Frequently only the final array slice of the customized summing operation
>> is wanted.  So I propose several new options:
>>
>> opt = 4 ; when _FillValue is encountered, return _FillValue.
>> opt = 5 ; return sum only up to the first encountered _FillValue.
>> opt = 6 ; return sum only following the last encountered _FillValue.
>> opt = 7 ; treat _FillValue as numeric zero, and return only the final sum.
>>
>> The first three existing options return an array of the same type and
>> dimensionality as *x*.  These four new options would return an array of
>> one lesser rank than x; the summing dimension would be removed.
>>
>> Options 4, 6, and 7 would return exactly the same result as taking the
>> "last" array slice on the summing dimension, of options 0, 1, and 2
>> respectively.
>>
>> Option 5 would be special.  Summing would end on the FIRST encountered
>> _FillValue, and that result would be returned.  Option 5 would be exactly
>> the same as option 6 with reversed input ordering on the summing
>> dimension.  Option 5 is included mainly for symmetry and completeness.
>>
>> To be consistent with current option 1, _FillValue is explicitly returned
>> when:
>>
>> opt = 5 and the first input element is _FillValue.
>> opt = 6 and the last input element is _FillValue.
>>
>> These new options would simplify user code in some cases, such as
>> Rashed's case today.  In large array applications, these options could
>> also reduce memory consumption and run time.
>>
>> --Dave
>>
>
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