From: Levi Waldron <leviwaldron_at_gmail.com>

Date: Fri, 27 Jun 2008 16:52:41 -0400

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 27 Jun 2008 - 20:56:42 GMT

Date: Fri, 27 Jun 2008 16:52:41 -0400

This one should be easy but it's giving me a hard time mostly because tapply
puts the results in a list. I want to calculate the cumulative sum of a
variable in a dataframe, but with the accumulation only within each level of
a factor. For a very simple example, take:

*> df <-
*

data.frame(x=c(rep(1,5),rep(2,5),rep(3,5)),fac=gl(3,5,labels=letters[1:3]))

*> df
*

x fac

1 1 a

2 1 a

3 1 a

4 1 a

5 1 a

6 2 b

7 2 b

8 2 b

9 2 b

10 2 b

11 3 c

12 3 c

13 3 c

14 3 c

15 3 c

> answer

x fac willdo ideal

1 1 a 1 0 2 1 a 2 1 3 1 a 3 2 4 1 a 4 3 5 1 a 5 4 6 2 b 2 0 7 2 b 4 2 8 2 b 6 4 9 2 b 8 6 10 2 b 10 8 11 3 c 3 0 12 3 c 6 3 13 3 c 9 6 14 3 c 12 9 15 3 c 15 12 [[alternative HTML version deleted]] ______________________________________________R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 27 Jun 2008 - 20:56:42 GMT

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