[R] creating a count variable in R

[JonC]

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 


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