Applying a function to all combinations of factors

you could use something  like

by(data, list(data1$day, data1$hour), function(x) cor(x[,"var1"], x[,
"var2"]))

This will return a list and then you can unlist and turn to matrix

HTH
Is there a way to apply a function, say cor(), to each combination of some
number of variables, and this, without using loops?

For example, I have day, hour, var1 and var2. How could I compute
cor(var1,var2) for each day*hour combination and obtain a matrix with day,
hour and the cor value for each combination?

Thanks for your time,

Marc

==================Marc B?lisle
Professeur adjoint
Chaire de recherche du Canada en ?cologie spatiale et en ?cologie du
paysage
D?partement de biologie
Universit? de Sherbrooke
2500 Boul. de l'Universit?
Sherbrooke, Qu?bec
J1K 2R1 Canada

T?l: +1-819-821-8000 poste 1313
Fax: +1-819-821-8049
Courri?l: Marc.M.Belisle at USherbrooke.ca

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Applying a function to all combinations of factors

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