Home -> Usenet -> comp.databases.theory -> Re: Aggregates: Largest Groups

Re: Aggregates: Largest Groups

From: David Fetter <david_at_fetter.org>
Date: Mon, 22 Mar 2010 16:48:16 -0500
Message-ID: <4oqdneNxef09eDrWnZ2dnUVZ_uOdnZ2d_at_speakeasy.net> 






Gene Wirchenko <genew_at_ocis.net> wrote:

> On Mon, 22 Mar 2010 16:12:50 -0500, david_at_fetter.org (David Fetter)
> wrote:
> 




>>Gene Wirchenko <genew_at_ocis.net> wrote:


>>> On Mon, 22 Mar 2010 15:42:09 -0500, david_at_fetter.org (David Fetter)

>>> wrote:

>>> 

>>>>Let's say I have a traffic monitoring system.  The stream of data

>>>>coming in records a timestamp and a speed for each vehicle.

>>>>

>>>>I'd like to know what all the groups of vehicles larger than X whose

>>>>with average speed over Y is.

>>>>

>>>>Any ideas how to approach this?

>>> 

>>>     First, define your terms.  What is a group?  What does "larger

>>> than X" mean?  (Size of vehicle?  Number of vehicles in the group?)

>>

>>Number of vehicles in the group.

> 


>     And what is a group?



Those vehicles, grouped in time, whose average speed is >= Y.



Let's say we're looking for groups of 20 or more vehicles whose
average speed is >= 175 kph.



The first 20 vehicles pass by at 200 kph, then another 20 pass at 100,
each at distinct times.



When vehicle 6 of the slower bunch passes, the average speed of cars
up until now is (20*200+6*100)/26 or ~176.92 kph.  Vehicle 7 passes,
and the average is now ~174.07, which is under 175, so the first group
has 26 vehicles in it, and we're now looking to start the next group.



Cheers,


David.

-- 
David Fetter <david_at_fetter.org> http://fetter.org/
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Received on Mon Mar 22 2010 - 22:48:16 CET












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