[R] Data Manipulation, add frequency index

[Gabor Grothendieck]

See ?ave and ?seq_along

DF <- data.frame(Name = c("Mary", "Mary", "Mary", "Sam", "Sam",
   "John", "John", "John", "John"), stringsAsFactors = FALSE)
DF$index <- ave(1:nrow(DF), DF$Name, FUN = seq_along)


On Sat, Nov 8, 2008 at 5:43 AM, jie feng <jiefeng222 at gmail.com> wrote:
> Hi, there,
>
> I have a simple data manipulation question for you. Thank you for your help!
>
>  Suppose that I have this data about people appearing in a class
>
>
> Mary
> Mary
> Mary
> Sam
> Sam
> John
> John
> John
> John
>
> Then I want to find out what exact time(s) the student appears at the
> moment such as
>
>  Mary 1
> Mary 2
> Mary 3
> Sam 1
> Sam 2
> John 1
> John 2
> John 3
> John 4
>
> the fifth row shows tha Sam show the second times at the that moment.
>
> How can I manipulate the data in this way. Suppose that now I just have
> "name" variable and want to add a colume of frequency?
>
> Best
>
> Jie
>
>        [[alternative HTML version deleted]]
>
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