[R] how to count unique observations by variables

[ronggui]

How about this:

> df1=data.frame(v1=c(1,1,2,3,2,4,1))
> df1$v2 <- ave(df1$v1,df1$v1,FUN=length)
> df1
  v1 v2
1  1  3
2  1  3
3  2  2
4  3  1
5  2  2
6  4  1
7  1  3


On Thu, Oct 16, 2008 at 1:27 PM, Lijiang Guo <lijguo at gmail.com> 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).
>
> Could someone tell me how to do this?
>
> regards,
> Lijiang
>
>
> --
>
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-- 
HUANG Ronggui, Wincent
Tel: (00852) 3442 3832
Ph.D. Candidate, CityU of HK
Master of sociology, Fudan University, China
Bachelor of Social Work, Fudan University, China
Personal homepage: http://ronggui.huang.googlepages.com/