[R] selecting maximum values

From: alessandro carletti <alxmilton_at_yahoo.it>
Date: Thu 05 May 2005 - 01:43:02 EST


Sorry for disturbing you with another newbie question! I have a data frame about coastal waters quality parameters: for some parameters (e.g. NH3) I have only 1 observation for each sampling station and each sampling date, while in other cases (chlorophyll) I have 1 obs for each meter-depth for each station and date. How can I select only the max chlorophyll value for each station/date?

example

row  station         date        depth     chlorophyll
1     Castagneto      21/06/01     -0.5         2.0
2     Castagneto      21/06/01     -1.5         2.2
3     Castagneto      21/06/01     -2.5         2.4
4     Castagneto      21/06/01     -3.5         2.1
5     Ancona          23/06/01     -0.5         2.4
6     Ancona          23/06/01     -1.5         2.5
7     Ancona          23/06/01     -2.5         2.2
8     Ancona          23/06/01     -3.5         2.1
9     Ancona          23/06/01     -4.5         1.9
...

I'd like to select only row 3 and 6, the ones with max chlorophyll values, or have the mean for the rows 1:4 and 5:9

Thanks



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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu May 05 02:11:36 2005

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