Use cumsum() to count the change points:
> Date_var <- as.Date(rep(c("2011-02-04","2011-02-07","2011-01-29"),
c(2,3,1)))
> data.frame(Date_var, count=cumsum(c(TRUE,
Date_var[-1]!=Date_var[-length(Date_var)])))
Date_var count
1 2011-02-04 1
2 2011-02-04 1
3 2011-02-07 2
4 2011-02-07 2
5 2011-02-07 2
6 2011-01-29 3
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -----Original Message-----
> From: r-help-boun...@r-project.org
> [mailto:r-help-boun...@r-project.org] On Behalf Of JonC
> Sent: Thursday, March 03, 2011 1:58 PM
> To: r-help@r-project.org
> Subject: [R] creating a count variable in R
>
> Hi R helpers,
>
> I'm trying to create a count in R , but as there is no retain
> function like
> in SAS I'm running into difficulties.
>
> I have the following :
>
> Date_var and wish to obtain
> Date_var
> Count_var
> 01/01/2011
> 01/01/2011
> 1
> 01/01/2011
> 01/01/2011
> 2
> 02/01/2011
> 02/01/2011
> 1
> 02/01/2011
> 02/01/2011
> 2
> 02/01/2011
> 02/01/2011
> 3
> 02/01/2011
> 02/01/2011
> 4
> 03/01/2011
> 03/01/2011
> 1
> 03/01/2011
> 03/01/2011
> 2
> 03/01/2011
> 03/01/2011
> 3
> 03/01/2011
> 03/01/2011
> 4
> 03/01/2011
> 03/01/2011
> 5
> 03/01/2011
> 03/01/2011
> 6
> 03/01/2011
> 03/01/2011
> 7
>
> As can be seen above the count var is re initialised every
> time a new date
> is found. I hope this is easy.
>
> Many thanks in advance for assistance. It is appreciated.
>
> Cheers
>
> Jon
>
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/creating-a-count-variable-in-R-t
p3334288p3334288.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
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>
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