Dear friends,
I have a question do not know how to resolve.
I have a big matrix composed of different columns (I use N here). A column is
"species" and another one is "latitudes". Now, I want to know how I can get the
number of different "latitudes" for every "species". I have tried to split the
matrix according to species (X<-split(N, N$species) and then use sapply(X,
function(m){nlevels(m$latitudes)}) to get that. But the result shows the total
factor numbers of "latitudes" but not the factor numbers of every species I
splitted. Also, I have tried to use tapply(N$latitudes, N$species, nlevels) to
do this. The result is the same. I am confused about this. Can someone help me
with that? Thank you very much!
Best regards,
Yichun
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