From: jim holtman <jholtman_at_gmail.com>

Date: Sat, 12 Jul 2008 07:37:04 -0400

*> # create a list of the indices of the data grouped by 'cat'
*

> split(seq(nrow(x)), x$cat)

$A

[1] 4 6 8 9 10 11 12

18 B 18 0.1031842

20 B 20 0.6401010

Date: Sat, 12 Jul 2008 07:37:04 -0400

*> x <- data.frame(cat=sample(LETTERS[1:3],20,TRUE),a=1:20, b=runif(20))
**> x
*

cat a b

1 B 1 0.65472393 2 C 2 0.35319727 3 B 3 0.27026015 4 A 4 0.99268406 5 C 5 0.63349326 6 A 6 0.21320814 7 C 7 0.12937235 8 A 8 0.47811803 9 A 9 0.92407447 10 A 10 0.59876097 11 A 11 0.97617069 12 A 12 0.73179251 13 B 13 0.35672691 14 C 14 0.43147369 15 C 15 0.14821156 16 C 16 0.01307758 17 B 17 0.71556607 18 B 18 0.10318424 19 C 19 0.44628435 20 B 20 0.64010105

> split(seq(nrow(x)), x$cat)

$A

[1] 4 6 8 9 10 11 12

$B

[1] 1 3 13 17 18 20

$C

[1] 2 5 7 14 15 16 19

*> # or do you want the data
*

> split(x, x$cat)

$A

cat a b

4 A 4 0.9926841 6 A 6 0.2132081 8 A 8 0.4781180 9 A 9 0.9240745 10 A 10 0.5987610 11 A 11 0.9761707 12 A 12 0.7317925 $B cat a b 1 B 1 0.6547239 3 B 3 0.2702601 13 B 13 0.3567269 17 B 17 0.7155661

18 B 18 0.1031842

20 B 20 0.6401010

$C

cat a b

2 C 2 0.35319727 5 C 5 0.63349326 7 C 7 0.12937235 14 C 14 0.43147369 15 C 15 0.14821156 16 C 16 0.01307758 19 C 19 0.44628435

On Sat, Jul 12, 2008 at 3:32 AM, <rkevinburton_at_charter.net> wrote:

> I have search the archive and I could not find what I need so I will try to ask the question here.

*>
**> I read a table in (read.table)
**>
**> a <- read.table(.....)
**>
**> The table has column names like DayOfYear, Quantity, and Category.
**>
**> The values in the row for Category are strings (characters).
**>
**> I want to get all of the rows grouped by Category. The number of unique category names could be around 50. Say for argument sake the number of categories is exactly 50. Can I somehow get a vector of length 50 containing the rows corresponding to the category (another vector)? I realize I can access any row a[i]$Category (right?). But I wanta vector containing the rows corresponding to each distinct Category name.
**>
**> Thank you.
**>
**> Kevin
**>
**> ______________________________________________
**> R-help_at_r-project.org mailing list
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**> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
**> and provide commented, minimal, self-contained, reproducible code.
**>
*

-- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem you are trying to solve? ______________________________________________ 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 Sat 12 Jul 2008 - 11:42:04 GMT

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