[R] Odp: Sequence of ordered variable to add as column

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 19.03.2010 11:25:12:

> Hello all,
> 
> As an example, consider the following dataframe
> 
> > df<-data.frame(id=c("b","b","a","a","a"),ord=c(2,1,1,3,2))
> > dates<-as.Date(c("02/27/92", "02/27/92", "01/14/92", "02/28/92", 
"02/01/
> 92"),"%m/%d/%y")
> > df$dates<-dates
> 
> which was ordered with
> 
> > df<-df[order(df$id,df$dates),]
> 
> Now I would like to add a column containing a sequence (disregarding
> ties) that represents the order of the variable
> "dates" in each case of the variable "id", resulting in this dataframe:
> 
> > seq.id<-c(1,2,3,1,2)
> > df$seq.id<-seq.id
> 
>   id ord      dates seq.id
> 3  a   1 1992-01-14      1
> 5  a   2 1992-02-01      2
> 4  a   3 1992-02-28      3
> 1  b   2 1992-02-27      1
> 2  b   1 1992-02-27      2

Here is one option but I believe others will come with more clever one.

df$seq.id<-unlist(tapply(as.numeric(df$id), df$id, order))

Regards
Petr



> 
> 
> Thanks in advance,
> 
> Duarte Viana
> 
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