Basic stratification calculations

vito muggeo wrote:

Hi,
if I understand correctly, tapply() is your friend here,
vito
dvrecko at sfu.ca wrote:

Hi. I'm a student at SFU in Canada. The basic thing I want to do is
calculate means of different strata. I have 2 vectors. One has the 
values I
want to take the means from, the other is the four strata I am 
interested
in. So I essentially want to break up the information vector into 
the four
strata and calculate four means, one for each stratum. How can I do 
this in
a reasonable way?


Thanks very much.
Dean Vrecko

PS: Incidentally I forget how to see the code of functions. Does 
anyone
remember the command to do this?

Would split(y,f) be of some help here? And then you could find the 
mean for each level of f:

y.split <- split(y,f)
mean(y.split$"0")
mean(y.split$"1")
mean(y.split$"2")
mean(y.split$"3")