aggregate function

Here is an example using 'data.table'"

x <- read.table(text = "param       case1
+ 1               a
+ 2               b
+ 2               c
+ 2               d
+ 3               e
+ 4               f", header = TRUE, as.is = TRUE)
And the aggregate version:

 > aggregate(x$case1, x["param"], FUN=paste, collapse=",")
   param     x
1     1     a
2     2 b,c,d
3     3     e
4     4     f

( Generally one uses the "[[" function for extraction, but using  "["  
returns a list which is what aggregate is designed to process as its  
second argument, whereas you would get an error with either of these:

aggregate(x$case1, x$param, FUN=paste, collapse=",")
aggregate(x$case1, x[["param"]], FUN=paste, collapse=",")
  )
require(data.table)
x <- data.table(x)
x[
+     , list( case1 = paste(case1, collapse = ','))
+     , by = param
+  ]
    param case1
[1,]     1     a
[2,]     2 b,c,d
[3,]     3     e
[4,]     4     f

On Wed, Dec 21, 2011 at 11:26 AM, Mary Kindall  
<mary.kindall at gmail.com> wrote:
Hi
I have a data frame with values in following format.

param       case1
1               a
2               b
2               c
2               d
3               e
4               f

how to use aggregate so that it I only one row for each 'param'  
value.

the output for the above input should be

param     case1
1      a
2      b,c,d
3      e
4      f

Thanks
M

--
-------------
Mary Kindall
Yorktown Heights, NY
USA

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______________________________________________
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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.
David Winsemius, MD
West Hartford, CT

aggregate function

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