On Sep 19, 2009, at 5:39 AM, Sam Player wrote:
#I have a dataset with two factor. I want to combine those factors
into a single factor and count the number of data values for each
new factor. The following gives a comparable dataframe:
a <- rep(c("a", "b"), c(6,6))
b <- rep(c("c", "d"), c(6,6))
df <- data.frame(f1=a, f2=b, d=rnorm(12))
df
# I use the 'interaction' function to combine factors f1 and f2:
df2 <- data.frame(f3=interaction(df[,"f1"], df[,"f2"]), d=df[,"d"])
df2
# A count of the first data.frame using factor f1 returns the kind
of results I am looking for:
count <- as.data.frame(table(df$f1))
count
# Var1 Freq
#1 a 6
#2 b 6
# As does a count using factor2:
count2 <- as.data.frame(table(df$f2))
count2
# Var1 Freq
#1 a 6
#2 b 6
# The same procedure on the second dataframe does not treat the
levels of factor f3 discreetly, instead giving all possible
combinations of f1 and f2.
We appear to have a different understanding of the term "discrete".
The interaction function produces all possible combinations of factors
and then table() counts the occurrences of such.
count3 <- as.data.frame(table(df2$f3))
count3
# Var1 Freq
#1 a.c 6
#2 b.c 0
#3 a.d 0
#4 b.d 6
I need the results to be:
# Var1 Freq
#1 a 6
#2 b 6
Puzzled. You already have such. Why would you want the interaction
function to behave differently?
Did you just want to create a label from f1 and f2? That can be
achieved:
> df2 <- df
> df2$f12 <- with( df2, paste(f1,f2,sep=".") )
> df2
f1 f2 d f12
1 a c -0.52902802 a.c
2 a c -1.07351118 a.c
3 a c 0.63463011 a.c
4 a c 0.26857599 a.c
5 a c 1.57677999 a.c
6 a c 1.08645153 a.c
7 b d -0.60400852 b.d
8 b d -0.06611533 b.d
9 b d 1.00787048 b.d
10 b d 1.48289305 b.d
11 b d 0.54658888 b.d
12 b d -0.67630052 b.d
> count3 <- as.data.frame(table(df2$f12))
> count3
Var1 Freq
1 a.c 6
2 b.d 6
# Any suggestions?
--
Sam Player, B.Sc.(Hons.) B.A.
Ph.D. Candidate, Faculty of Agriculture, Food & Natural Resources,
University of Sydney
Email: spla...@usyd.edu.au
Agroecosystems Research Group
Room 214 J.R.A. McMillan Building A05
University of Sydney NSW 2006, Australia
Angkor Research Program
Room 305 Old Teachers College A22
University of Sydney NSW 2006, Australia
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT
______________________________________________
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