R help - Jun 2008 - cumulative sum of within levels of a dataframe

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

I'd like to create another column in the dataframe so it looks like this,
and make sure that the cumulative sums still match the right levels of the
factor.  I've included a "willdo" column that's just a
cumulative sum, and
an "ideal" column that's the cumulative sum minus the current
value - the
column headings are self explanatory.
> 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]]

Just use ?unlist

df$willdo <- unlist(tapply(df$x, df$fac, cumsum))
df$ideal <- df$willdo - df$x

Levi Waldron wrote:
> 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
> 
> I'd like to create another column in the dataframe so it looks like
this,
> and make sure that the cumulative sums still match the right levels of the
> factor.  I've included a "willdo" column that's just a
cumulative sum, and
> an "ideal" column that's the cumulative sum minus the current
value - the
> column headings are self explanatory.
> 
>> 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.

On Fri, 2008-06-27 at 16:52 -0400, Levi Waldron wrote:
> 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$willdo <- unlist(tapply(df$x, df$fac, cumsum))
> df$ideal <- df$willdo - df$x
> df
   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

HTH

G
> 
> > 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
> 
> I'd like to create another column in the dataframe so it looks like
this,
> and make sure that the cumulative sums still match the right levels of the
> factor.  I've included a "willdo" column that's just a
cumulative sum, and
> an "ideal" column that's the cumulative sum minus the current
value - the
> column headings are self explanatory.
> 
> > 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.
-- 
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 Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
 ECRC, UCL Geography,          [f] +44 (0)20 7679 0565
 Pearson Building,             [e] gavin.simpsonATNOSPAMucl.ac.uk
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Try this:

df$wildo <- ave(df$x, df$fac, FUN = cumsum)


On Fri, Jun 27, 2008 at 4:52 PM, Levi Waldron <leviwaldron at gmail.com>
wrote:
> 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
>
> I'd like to create another column in the dataframe so it looks like
this,
> and make sure that the cumulative sums still match the right levels of the
> factor.  I've included a "willdo" column that's just a
cumulative sum, and
> an "ideal" column that's the cumulative sum minus the current
value - the
> column headings are self explanatory.
>
>> 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.
>