[R] Two basic data manipulation questions (counting and aggregating)
Greg Snow
Greg.Snow at intermountainmail.org
Fri Apr 13 16:38:57 CEST 2007
For the 1st question, if every record with the same id is together in a
block, then
> mydf$counter <- unlist( tapply( mydf$type, mydf$id, rank, tie='first'
) )
Should give you your counter column
If the id's are not in blocks then try:
> mydf$counter <- ave(tmp$type, factor(tmp$id), FUN=function(x) rank(x,
tie='first'))
For the second question, look at the collapse argument to paste. Using
paste with collapse='' should give you the scalar that you can use with
aggregate.
Hope this helps,
--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at intermountainmail.org
(801) 408-8111
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Julien Barnier
> Sent: Friday, April 13, 2007 5:08 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Two basic data manipulation questions (counting
> and aggregating)
>
> Dear R users,
>
> I hav two basic data manipulations questions that I can't resolve.
>
> My data is a data frame which look like the following :
>
> id type
> 10002 "7"
> 10061 "1"
> 10061 "1"
> 10061 "4"
> 10065 "7"
> 10114 "1"
> 10114 "1"
> 10114 "4"
> 10136 "7"
> 10136 "2"
> 10136 "2"
>
>
> First, I would like to create a "counter" variable which will
> count the rank of each row inside each "id" level, ie something like :
>
> id type counter
> 10002 "7" 1
> 10061 "1" 1
> 10061 "1" 2
> 10061 "4" 3
> 10065 "7" 1
> 10114 "1" 1
> 10114 "1" 2
> 10114 "4" 3
> 10136 "7" 1
> 10136 "2" 2
> 10136 "2" 3
>
> Is there a straightforward way to do that, without using
> several "for" loops ?
>
> The second thing I would like to do is to aggregate the first
> data.frame by concatenating the 'type' values for each 'id',
> ie I'd like to obtain something like :
>
> id value
> 10002 7
> 10061 114
> 10065 7
> 10114 114
> 10136 722
>
> I have tried the "aggregate" function, but it doesn't work
> because the "paste" function doesn't return a scalar value.
> Using tapply seems to work, but is not straightforward, and I
> wanted to know if there is a simple way to do this.
>
> Thanks in advance for any help.
>
> --
> Julien
>
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