Thanks Ross.  Yes, upon your remark it seems that maybe I need to be
selecting first for the best available location, and then by the time stamp
nearest to 12pm.  It seems like tapply(), or aggregate() or aggregate.ts()
might be applicable, but I'm working through trying different functions and
have yet to find what works.  Suggestions on what function to start with
would be appreciated.  

 

Tim Sippel (MSc)

School of Biological Sciences

Auckland University

Private Bag 92019

Auckland 1020

New Zealand

+64-9-373-7599 ext. 84589 (work)

+64-9-373-7668 (Fax)

+64-21-593-001 (mobile)

 

  _____  

From: Ross Darnell [mailto:r.darnell@uq.edu.au] 
Sent: 08 August 2007 12:43
To: Tim Sippel; r-help@stat.math.ethz.ch
Subject: RE: [R] Conditional subsetting

 

 

Assuming *A* animal can only be in one location at any one time, I don't
understand how once you have selected the location nearest 12pm how you can
select based on the type of location?
Do you mean to select on location before timei.e. from the best location
visited that day which was closest to 12pm?

Perhaps for condition 2  for a animal which.min(time-1200) (replace 1200
with properly defined timestamp representing 12:00pm)

Ross Darnell
 


-----Original Message-----
From: r-help-bounces@stat.math.ethz.ch on behalf of Tim Sippel
Sent: Wed 08-Aug-07 9:37 AM
To: r-help@stat.math.ethz.ch
Subject: [R] Conditional subsetting

Hello-

Upon searching the email archives and reading documentation I haven't found
what I'm looking for.  I have a dataset with a time/date stamp on a series
of geographic locations (lat/lon) associated with the movements of animals.
On some days there are numerous locations and some days there is only one
location.  Associated with each location is an indication that the quality
of the location is either "good", "poor", or "unknown".  For each animal, I
want to extract only one location for each day.  And I want the location
extracted to be nearest to 12pm on any given day, and highest quality
possible. 

So the order of priority for my extraction will be: 1. only one location per
animal each day; 2. the location selected be as close to 12pm as possible;
3. the selected location comes from the best locations available (ie. take
from pool of "good" locations first, or select from "poor" locations if a
"good" location isn't available, or "unknown" if nothing else is available).




I think aspect of this task that has me particularly stumped is how to
select only one location for each day, and for that location to be a close
to 12pm as possible. 



An example of my dataset follows:





DeployID



Date.Time



LocationQuality

Latitude

Longitude


STM05-1



28/02/2005 17:35



Good

-35.562

177.158


STM05-1



28/02/2005 19:44



Good

-35.487

177.129


STM05-1



28/02/2005 23:01



Unknown

-35.399

177.064


STM05-1



01/03/2005 07:28



Unknown

-34.978

177.268


STM05-1



01/03/2005 18:06



Poor

-34.799

177.027


STM05-1



01/03/2005 18:47



Poor

-34.85

177.059


STM05-2



28/02/2005 12:49



Good

-35.928

177.328


STM05-2



28/02/2005 21:23



Poor

-35.926

177.314




















































Many thanks for your input.  I'm using R 2.5.1 on Windows XP. 



Cheers,



Tim Sippel (MSc)

School of Biological Sciences

Auckland University

Private Bag 92019

Auckland 1020

New Zealand

+64-9-373-7599 ext. 84589 (work)

+64-9-373-7668 (Fax)

+64-21-593-001 (mobile)




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