On Oct 16, 2008, at 1:27 AM, Lijiang Guo wrote:
Dear R-helpers,
I have a data frame with 3 variables, each record is a unique
combination of
the three variables. I would like to count the number of unique
values of v3
in each v1, and save it as a new variable v4 in the same data frame.
e.g.
df1
[v1] [v2] [v3]
[1,] "a" "C" "1"
[2,] "b" "C" "2"
[3,] "c" "B" "3"
[4,] "a" "B" "3"
[5,] "b" "A" "2"
[6,] "c" "A" "1"
In this case, the 4th column would become (2, 1, 2, 2, 1, 2).
> txt <- ' v1 v2 v3
+ "a" "C" "1"
+ "b" "C" "2"
+ "c" "B" "3"
+ "a" "B" "3"
+ "b" "A" "2"
+ "c" "A" "1"'
df1 <- read.table(textConnection(txt), header=TRUE)
grps <- tapply(df1$v3, df1$v1,FUN=table)
# > sapply(grps,length)
# a b c
# 2 1 2
df1$v4 <- sapply(grps,length)[df1$v1]
df1
v1 v2 v3 v4
1 a C 1 2
2 b C 2 1
3 c B 3 2
4 a B 3 2
5 b A 2 1
6 c A 1 2
--
David Winsemius, MD
Heritage Labs
Could someone tell me how to do this?
regards,
Lijiang
--
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