Thanks Jim,
"Ave" does what I wanted.
It is simpler and probably more efficient
than unlisting Sn as I tried.
Still I remain puzzled with the structure
of the by() or tapply() output and how
to access the individual cumsums.
Yes the split command is useful for checking
the result.
Gerrit.
Op 12/7/2010 1:43 PM, jim holtman schreef:
Maybe 'ave' is what you were looking for:
d$cum<- ave(d$n, d$a, d$c, FUN = cumsum)
d
a b c n cum
1 1 1 1 11.1 11.1
2 2 1 1 21.1 21.1
3 3 1 1 31.1 31.1
4 4 1 1 41.1 41.1
5 5 1 1 51.1 51.1
6 1 2 1 12.1 23.2
7 2 2 1 22.1 43.2
8 3 2 1 32.1 63.2
9 4 2 1 42.1 83.2
10 5 2 1 52.1 103.2
11 1 3 1 13.1 36.3
12 2 3 1 23.1 66.3
13 3 3 1 33.1 96.3
14 4 3 1 43.1 126.3
15 5 3 1 53.1 156.3
16 1 1 2 11.2 11.2
17 2 1 2 21.2 21.2
18 3 1 2 31.2 31.2
19 4 1 2 41.2 41.2
20 5 1 2 51.2 51.2
21 1 2 2 12.2 23.4
22 2 2 2 22.2 43.4
23 3 2 2 32.2 63.4
24 4 2 2 42.2 83.4
25 5 2 2 52.2 103.4
26 1 3 2 13.2 36.6
27 2 3 2 23.2 66.6
28 3 3 2 33.2 96.6
29 4 3 2 43.2 126.6
30 5 3 2 53.2 156.6
On Tue, Dec 7, 2010 at 6:39 AM, Gerrit Draisma<gdrai...@xs4all.nl> wrote:
Dear R-users,
I have a dataset with categories and numbers.
I would like to compute and add cumulative numbers
to the dataset.
I do not understand the structure of by(...) or
tapply(...) output enough to handle it.
Here a small example
--------------
d<-expand.grid(a=1:5,b=1:3,c=1:2)
d$n = 10 * d$a + d$b +0.1* d$c
Sn<-by(d$n,list(d$a,d$c),cumsum)
str(Sn)
---------
List of 10
$ : num [1:3] 11.1 23.2 36.3
$ : num [1:3] 21.1 43.2 66.3
$ : num [1:3] 31.1 63.2 96.3
$ : num [1:3] 41.1 83.2 126.3
$ : num [1:3] 51.1 103.2 156.3
$ : num [1:3] 11.2 23.4 36.6
$ : num [1:3] 21.2 43.4 66.6
$ : num [1:3] 31.2 63.4 96.6
$ : num [1:3] 41.2 83.4 126.6
$ : num [1:3] 51.2 103.4 156.6
- attr(*, "dim")= int [1:2] 5 2
- attr(*, "dimnames")=List of 2
..$ : chr [1:5] "1" "2" "3" "4" ...
..$ : chr [1:2] "1" "2"
- attr(*, "call")= language by.default(data = d$n, INDICES = list(d$a,
d$c), FUN = cumsum)
- attr(*, "class")= chr "by
---------
# these give (a) lists of one numerical vector(a)
Sn[5,2]
Sn[cbind(d$a,d$c)]
# how to access the individual cumsum values?
# and assign them to d$Sn?
--------------
Thanks,
Gerrit.
---
Gerrit Draisma
Department of Public Health
Erasmus MC, University Medical Center Rotterdam
Room AE-235
P.O. Box 2040 3000 CA Rotterdam The Netherlands
Phone: +31 10 7043787 Fax: +31 10 7038474
http://mgzlx4.erasmusmc.nl/pwp/?gdraisma
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