Skip to content

Creating Observation ID

4 messages · Bill Venables, William Dunlap, Robert Baer

Original
Bill Venables
# 
Here is one way:

df <- data.frame(Value = rnorm(30),
                 Group = sample(c('A','B','C'), 30,
                 replace = TRUE))

## make a little function to do the job
iNumber <- function(f) {
  f <- as.factor(f)
  X <- outer(f, levels(f), "==")+0
  rowSums(X * apply(X, 2, cumsum))
}

## add the numbering column
df <- within(df, internalNumber <- iNumber(Group))

## Check that it works
Value Group internalNumber
1 -1.5014788     C              1
2  0.6035679     C              2
3 -0.6953930     C              3
4 -0.2413863     A              1
5 -0.1170961     A              2
6  1.5110721     C              4 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Robert Baer
Sent: Tuesday, 10 May 2011 7:22 AM
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


______________________________________________
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.
William Dunlap
# 
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
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


--------------------------------------------------
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