Calculate interaction for a big dataframe

Hi

you maybe could use paste

f1<-sample(letters[1:3], 10, replace=T)
f2<-sample(letters[4:7], 10, replace=T)
f3<-sample(letters[9:11], 10, replace=T)
interaction(f1, f2, f3, drop=T)

?  [1] c.e.j b.e.j a.e.j c.g.i a.f.j b.g.k a.e.i a.e.k a.d.j b.e.j
Levels: a.e.i c.g.i a.d.j a.e.j b.e.j c.e.j a.f.j a.e.k b.g.k

paste(f1, f2, f3, sep=".")

?  [1] "c.e.j" "b.e.j" "a.e.j" "c.g.i" "a.f.j" "b.g.k" "a.e.i" "a.e.k" "a.d.j"
[10] "b.e.j"

The difference is that interaction gives you directly factor, paste gives you character vector, but it may be convenient too for your purpose.

Regards
Petr

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Arnaud Michel
Sent: Monday, July 22, 2013 10:57 AM
To: R help
Subject: [R] Calculate interaction for a big dataframe

Hi

To calculate the value of the interaction between factors of a
dataframe df, does exist any function which could replace the function
when the dataframe df has the numbers of rows of df is large (~55000)
and also the numbers of combinaison of the three factors is large. The
calcul abort.
The function to calculate the interaction is :
as.numeric(interaction(df [,c(1:3)],drop=TRUE))

To complete the question and to calculate interaction beetween 3
factors f1, f2, f3, does it possible to calculate first f12 =
interaction
(f1,f2) and after calculate interaction (f12, f3).
It seems to me that yes.

Thanks for your help




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Michel ARNAUD
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