here is one way of doing it using 'ave':
dat - read.table(textConnection(mc yrret
+ 32902.233 01/01/1995 0.426
+ 15793.691 01/01/1995 0.024
+ 2375.868 01/01/1995 0.660
+ 54586.558 01/01/1996 0.497
+ 10674.900 01/01/1996 0.405
+859.656 01/01/1996 -0.033
+
I have a data frame, lets call it dat,
with 3 columns ( mc, yr, ret) which represent market
cap, year, and return. mc is a factor, mc, and ret are
real numbers.
I want to add a column to the data calculated as
follows.
For each year, I want to split the data by mc decile,
then calculate the mean
