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2007 Oct 12
1
Differencing data by groups
...otal there are ~350k rows of data
I can calculate simple EventNum averages using
meanobs<-aggregate(ctd[,7:9],by=list(EventNum=EventNum),mean)
But, I want to calculate a depth-weighted mean for salinity, temp and oxygen
for each EventNum. The depth-weighted mean is calculated as
Xbar = Sum{depth_interval*temp}/Sum(depth_intervals)
Where the depth interval is the differenced depths (i.e., 0.103-0.056 for
the second row of data).
I cannot seem to get diff to work the way I want it to - advice appreciated
Tom
Thomas J. Miller, Ph.D.
Professor
Chesapeake Biological Laboratory
University of Marylan...