R help - May 2014 - Creating a new column with the number of the observation

I have a "data frame" like this:

  Category Observed_value  A 100  A 130  A 140  B 90  C 80  D 120  D 130

I need to create an index column that show the number of the observation
for each category. I have three observations in the category A, one in
category B, one in category C and two in category D. The new matrix should
be like this:


  Category Observed_value Index  A 100 1  A 130 2  A 140 3  B 90 1  C 80 1
D 120 1  D 130 2

Please, could anyone help me with this problem?

Thank you.
-- 
Marcos Martins Santos
mmsantos.br@gmail.com
--
Skype: marcosmartinssantos

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Hi. Here is one approach:

x <- rep(c("A", "B", "C"), c(3,1,2))
DF <- data.frame(x, stringsAsFactors=FALSE)
cbind(DF, new_c=c(lapply(rle(DF$x)[[1]], function(x) 1:x), recursive=T))

Andrija


On Wed, May 28, 2014 at 10:46 PM, Marcos Santos
<mmsantos.br@gmail.com>wrote:
> I have a "data frame" like this:
>
>   Category Observed_value  A 100  A 130  A 140  B 90  C 80  D 120  D 130
>
> I need to create an index column that show the number of the observation
> for each category. I have three observations in the category A, one in
> category B, one in category C and two in category D. The new matrix should
> be like this:
>
>
>   Category Observed_value Index  A 100 1  A 130 2  A 140 3  B 90 1  C 80 1
> D 120 1  D 130 2
>
> Please, could anyone help me with this problem?
>
> Thank you.
> --
> Marcos Martins Santos
> mmsantos.br@gmail.com
> --
> Skype: marcosmartinssantos
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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