[R] Basic stratification calculations

[Clint Harshaw]

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?
>>
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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")

Clint


-- 
Clint Harshaw, PhD		EMail: charshaw at presby.edu	
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