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

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