On Mar 4, 2005, at 6:55 AM, Clint Harshaw wrote:
vito muggeo wrote:
Hi,
if I understand correctly, tapply() is your friend here,
vito
[EMAIL PROTECTED] 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?
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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")
You can automate this using aggregate:
> a <- rep(c('A','B','C','D'),25)
> b <- rnorm(100)
> aggregate(b,by=list(a),mean)
Group.1 x
1 A 0.1409995
2 B -0.1524387
3 C 0.3329184
4 D 0.1354157
Sean
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