R help - Nov 2009 - Unique observations

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shouldn't the first observation for Tree1 be " Tree1  leaves 
01-01-2009"?
> x <- read.table(textConnection("Tree  disease  date
+  Tree1  leaves  01-01-2009
+  Tree2  roots  13-09-2009
+  Tree1  roots  24-10-2009"), header=TRUE)
> closeAllConnections()
> # split by "Tree" and take first observation
> do.call('rbind', lapply(split(x, x$Tree), function(.tr) .tr[1,]))
       Tree disease       date
Tree1 Tree1  leaves 01-01-2009
Tree2 Tree2   roots 13-09-2009
>

On Wed, Nov 25, 2009 at 9:44 AM, John Lipkins
<john.lipkins at googlemail.com> wrote:
> Hey R list,
>
> A beginners question. How can I do the following:
>
> In my research population it is possible that several items can appear
> several times, measured on different moments in time. This is being
supplied
> in a total list with all observations identified by a number (per item) and
> a moment of observation (date). Now I want to make a unique list of this
> observation preserving the characteristics of the first observation. As
> example:
>
> ?Tree ?disease ?date
> ?Tree1 ?leaves ?01-01-2009
> ?Tree2 ?roots ?13-09-2009
> ?Tree1 ?roots ?24-10-2009
>
> Now I want to create a list of unique elements (in the example only once
> Tree1 and Tree2) with the first observed disease and date. For the example
> the result would look like:
>
> ?Tree ?disease ?date
> ?Tree1 ?roots ?24-10-2008
> ?Tree2 ?roots ?13-09-2009
>
> Can someone help me with this question?
>
> Thanks in advance.
> Kind regards,
>
> John
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

On Nov 25, 2009, at 9:44 AM, John Lipkins wrote:
> Hey R list,
>
> A beginners question. How can I do the following:
>
> In my research population it is possible that several items can appear
> several times, measured on different moments in time. This is being  
> supplied
> in a total list with all observations identified by a number (per  
> item) and
> a moment of observation (date). Now I want to make a unique list of  
> this
> observation preserving the characteristics of the first observation.  
> As
> example:
>
> Tree  disease  date
> Tree1  leaves  01-01-2009
> Tree2  roots  13-09-2009
> Tree1  roots  24-10-2009
>
> Now I want to create a list of unique elements (in the example only  
> once
> Tree1 and Tree2) with the first observed disease and date. For the  
> example
> the result would look like:
>
> Tree  disease  date
> Tree1  roots  24-10-2008
> Tree2  roots  13-09-2009
>
> Can someone help me with this question?
I think the function you will need include:

?as.Date  #to get the date field into sortable form
?order    #as in treedat2 <- treedat[ order(treedat$dt, treedat$Tree), ]
?duplicated  # as in treedat2[ !duplicated(treedat2(Tree), ]

--

David Winsemius, MD
Heritage Laboratories
West Hartford, CT