Hi John,
Something like this does what you are looking for:
z <- tapply(X[, 1], X[, 2], sum)
To have it in a matrix-like layout (similar to X):
data.frame(z, names(z))
Best,
Emmanuel
Le 30/05/2016 18:13, John Denton a écrit :
Hi all,
I have a two-column matrix, containing trees in one
Hi John.
This would have to be a data frame (not a matrix) as you could not have
different data types in your matrix. Try the function aggregate, e.g.:
obj<-data.frame(number=c(1,1.5,0.2,0.8,1.0,3.2),
tree=factor(c("A","A","B","C","A","B")))
obj ## data frame
