You can probably simplify this if you can assume that the dates are in sorted
order. Here is a way of doing it even if the days are in arbitrary order. The
count refers to the number of times that this date has appeared so far in the
sequence.
con <- textConnection("
01/01/2011
01/01/2011
02/01/2011
02/01/2011
02/01/2011
02/01/2011
03/01/2011
03/01/2011
03/01/2011
03/01/2011
03/01/2011
03/01/2011
03/01/2011
")
days <- scan(con, what = "")
close(con)
X <- model.matrix(~days-1)
XX <- apply(X, 2, cumsum)
dat <- data.frame(days = days, count = rowSums(X*XX))
dat
###
this uses days as a character string vector. If they are actual dates, then
convert them to character strings for this operation.
Bill Venables.
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf Of JonC
Sent: Friday, 4 March 2011 7:58 AM
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
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