I keep expecting R to have something analogous to the =count function in
Excel, but I can't find anything. I simply want to count the data for a
given category.
I've been using the ddply() function in the plyr package to summarize
means and st dev of my data, with this code:
ddply(NZ_Conifers,.(ElevCat, DataSource, SizeClass), summarise,
avgDensity=mean(Density), sdDensity=sd(Density), n=sum(Density))
and that gives me results that look like this:
ElevCat DataSource SizeClass avgDensity sdDensity n
1 Elev1 FIA Class1 38.67768 46.6673478 734.87598
2 Elev1 FIA Class2 27.34096 23.3232470 820.22879
3 Elev1 FIA Class3 15.38758 0.7088432 76.93790
4 Elev1 VTM Class1 66.37897 70.2050817 24958.49284
5 Elev1 VTM Class2 39.40786 34.9343269 11782.95152
6 Elev1 VTM Class3 21.17839 12.3487600 1461.30895
But, instead of "sum(Density)", I'd really like counts of "Density", so
that I know the sample size of each group. Any suggestions?
--
Christopher R. Dolanc
Post-doctoral Researcher
University of California, Davis
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