Basic stratification calculations

An embedded and charset-unspecified text was scrubbed...
Name: not available
Url: https://stat.ethz.ch/pipermail/r-help/attachments/20050304/3f92b339/attachment.pl
Hi,
if I understand correctly, tapply() is your friend here,

vito
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?

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html

====================================
Vito M.R. Muggeo
Dip.to Sc Statist e Matem `Vianelli'
Universit? di Palermo
viale delle Scienze, edificio 13
90121 Palermo - ITALY
tel: 091 6626240
fax: 091 485726/485612
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?

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! 
http://www.R-project.org/posting-guide.html

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	
Department of Mathematics	Phone: 864.833.8995
Presbyterian College		Fax: 864.938.3769
Clinton SC  29325		Office: Harrington-Peachtree Rm 412

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?

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! 
http://www.R-project.org/posting-guide.html

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