| Re: Duplicates - a new twist [message #39440 is a reply to message #39439] |
Tue, 18 May 2004 12:34   |
btt
Messages: 345
Registered: December 2000
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Senior Member |
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Bruce Bowler wrote:
> On Tue, 18 May 2004 08:32:45 -0400, Ben Tupper put fingers to keyboard and
> said:
>
>
>> Martin Doyle wrote:
>>
>>
>>> I have a dataset which consists of 3 columns: longitude, latitude and
>>> a value for an emission of an air pollutant. European countries report
>>> the emission of this pollutant for the latitude longitude coordinates
>>> which are within their countries. However, some of the latitude,
>>> longitude coordinates lie on the borders of countries and therefore an
>>> emission is sometimes reported by 2 or more countries for the same
>>> coordinate (i,e. There are multiple instances of the same coordinate
>>> within the dataset).
>>>
>>> What I need to do is to look through the dataset and sum the emissions
>>> when the coordinate is the same, resulting in a dataset with unique
>>> coordinates and a total emission for each grid point.
>>>
>>> Does anyone have any ideas about how to go about this? I've seen posts
>>> on this newsgroup which have had problems with duplicate values in one
>>> column of data, but I'm unsure about how to go about it when there are
>>> 2 columns which need to be examined.
>>>
>>
>> Hello,
>>
>> You should consider using GRID_INPUT. This is from the docs...
>>
>>
>> The GRID_INPUT procedure preprocesses and sorts two-dimensional
>> scattered data points, and removes duplicate values.
>>
>> Ben
>
>
> But Ben, he doesn't want to remove dup's, he wants to sum them...
> (personally, I would have thought that average was better based on the
> description, but what the heck...)
>
Awww! I was duped!
The DUPLICATES keyword for GRID_INPUT does everything BUT 'SUM'. Then
again, setting DUPLICATES = 'all' should sort the data pairs so the
duplicates are adjacent in the list. Then finding the pairwise
difference between consecutive points should reveal where the duplicates
are located. I have a vague memory of making a feature request for an
INDEX output keyword that has the indices of the points retained by
GRID_INPUT (relative to input vectors.) I remember getting a response
at the time, but can't recall what it was... and obviously there is no
such keyword in the current release.
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