Aggregate and Weighted Mean in R

Question

I\'m trying to calculate asset-weighted returns by asset class. For the life of me, I can\'t figure out how to do it using the aggregate command.

My data frame look

Answer 1

A data.table solution, will be faster than plyr

library(data.table)
DT <- data.table(dat)
DT[,list(wret = weighted.mean(return,assets)),by=assetclass]
##    assetclass        wret
## 1:          A -0.05445455
## 2:          E -0.56614312
## 3:          D -0.43007547
## 4:          B  0.69799701
## 5:          C  0.08850954