[R] Creating Observation ID

[Robert Baer]

Thanks Bill and William.  Both solutions work, and both have introduced me 
to whole new R functions which I'm still wrapping my head around.

What a great resource this list is.

Thanks again,
Rob

------------------------------------------
Robert W. Baer, Ph.D.
Professor of Physiology
Kirksville College of Osteopathic Medicine
A. T. Still University of Health Sciences
800 W. Jefferson St.
Kirksville, MO 63501
660-626-2322
FAX 660-626-2965


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From: "William Dunlap" <wdunlap at tibco.com>
Sent: Monday, May 09, 2011 5:17 PM
To: "Robert Baer" <rbaer at atsu.edu>; <R-help at r-project.org>
Subject: RE: [R] Creating Observation ID

> Does the following work for you?
>
> > df2 <- transform(df, ObsID=ave(rep(0,length(Group)), Group,
> FUN=seq_along))
> > head(df2)
>        Value Group ObsID
> 1 -0.0025132     B     1
> 2 -1.2456156     A     1
> 3 -2.0531704     B     2
> 4  1.5861770     B     3
> 5  0.1900908     A     2
> 6  0.7197067     B     4
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
>> -----Original Message-----
>> From: r-help-bounces at r-project.org
>> [mailto:r-help-bounces at r-project.org] On Behalf Of Robert Baer
>> Sent: Monday, May 09, 2011 2:22 PM
>> To: R-help at r-project.org
>> Subject: [R] Creating Observation ID
>>
>> If I have a data frame something like:
>> Value=rnorm(30)
>> Group = sample(c('A','B','C'), 30, replace=TRUE)
>> df = data.frame(Value, Group)
>>
>> It seems like it should be simple to create an 'ObsID' column
>> which indicates the observation order of each Value within
>> each of the 3 groups.  Somehow, I can't quite see how to do
>> it without manually sub-setting the parent data frame and
>> then putting it back together again.
>>
>> Anyone able to get me started on a cleaner (more R-like) approach?
>>
>> Thanks,
>>
>> Rob
>>
>> ------------------------------------------
>> Robert W. Baer, Ph.D.
>> Professor of Physiology
>> Kirksville College of Osteopathic Medicine
>> A. T. Still University of Health Sciences
>> 800 W. Jefferson St.
>> Kirksville, MO 63501
>> 660-626-2322
>> FAX 660-626-2965
>>
>> [[alternative HTML version deleted]]
>>
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>