[R] Switching labels on a factor

[Muenchen, Robert A (Bob)]

Chris,

Argh!!! I was writing a reply just now insisting that the output below
makes no sense when it finally hit me: the first line of output from the
unclass function is just the data and bears no relationship whatsoever
with the order of the "m" and "f" below it. I had gotten the idea that
it picked up on the first value and so displayed the label to match. I
don't even want to think about how much time I spent working on a
"problem" that was nonexistent!

Thank you very much for your help!

Bob

> unclass(mydata$gR)
[1] 2 2 2 2 1 1 1 1
attr(,"levels")
[1] "m" "f"


=========================================================
Bob Muenchen (pronounced Min'-chen), Manager 
Statistical Consulting Center
U of TN Office of Information Technology
200 Stokely Management Center, Knoxville, TN 37996-0520
Voice: (865) 974-5230 
FAX: (865) 974-4810
Email: muenchen at utk.edu
Web: http://oit.utk.edu/scc, 
News: http://listserv.utk.edu/archives/statnews.html
=========================================================


-----Original Message-----
From: Chris Andrews [mailto:candrews at buffalo.edu] 
Sent: Monday, December 18, 2006 12:05 PM
To: Muenchen, Robert A (Bob)
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] Switching labels on a factor


Bob,

This is I think exactly what one wants to have happen.  The first four
observations are still women.  Both the labels and the underlying
integers should change.  (If you want to give all the people sex
changes, try Relevel in the Epi package.

mydata$afterthechange <- Relevel(mydata$gender, list(m="f", f="m"))
mydata


  workshop gender q1 q2 q3 q4 gR afterthechange
1        1      f  1  1  5  1  f              m
2        2      f  2  1  4  1  f              m
3        1      f  2  2  4  3  f              m
4        2      f  3  1 NA  3  f              m
5        1      m  4  5  2  4  m              f
6        2      m  5  4  5  5  m              f
7        1      m  5  3  4  4  m              f
8        2      m  4  5  5 NA  m              f


unclass(mydata$afterthechange)
[1] 1 1 1 1 2 2 2 2
attr(,"levels")
[1] "m" "f"

Chris


Date: Fri, 15 Dec 2006 15:34:15 -0500
From: "Muenchen, Robert A (Bob)" <muenchen at utk.edu>
Subject: [R] Switching labels on a factor
To: <R-help at stat.math.ethz.ch>
Message-ID:
	
<7270AEC73132194E8BC0EE06B35D93D84A061C at UTKFSVS3.utk.tennessee.edu>
Content-Type: text/plain;	charset="US-ASCII"

Hi All,

I'm perplexed by the way the unclass function displays a factor whose
labels have been swapped with the relevel function. I realize it won't
affect any results and that the relevel did nothing useful in this
particular case. I'm just doing it to learn ways to manipulate factors.
The display of unclass leaves me feeling that the relevel had failed.

I've checked three books & searched R-help, but found no mention of this
particular issue.  

The program below demonstrates the problem. Is this a bug, or is there a
reason for it to work this way?

Thanks,
Bob

mystring<-
("id,workshop,gender,q1,q2,q3,q4
 1,1,f,1,1,5,1
 2,2,f,2,1,4,1
 3,1,f,2,2,4,3
 4,2,f,3,1, ,3
 5,1,m,4,5,2,4
 6,2,m,5,4,5,5
 7,1,m,5,3,4,4
 8,2,m,4,5,5,9")
mydata<-read.table(textConnection(mystring),
   header=TRUE,sep=",",row.names="id",na.strings="9")
mydata

# Create a gender Releveled variable, gR. 
# Now 1=m, 2=f
mydata$gR <- relevel(mydata$gender, "m")

# Print the data to show that the labels of gR match those of gender.
mydata

# Show that the underlying codes have indeed reversed.
as.numeric(mydata$gender)
as.numeric(mydata$gR)

# Unclass the two variables to see that print order 
# implies that both the codes and labels have
# flipped, cancelling each other out. For gR,
# m appears to be associated with 2, and f with 1
unclass(mydata$gender)
unclass(mydata$gR)

=========================================================
  Bob Muenchen (pronounced Min'-chen), Manager  
  Statistical Consulting Center
  U of TN Office of Information Technology
  200 Stokely Management Center, Knoxville, TN 37996-0520
  Voice: (865) 974-5230  
  FAX:   (865) 974-4810
  Email: muenchen at utk.edu
  Web:   http://oit.utk.edu/scc, 
  News:  http://listserv.utk.edu/archives/statnews.html




-- 
Christopher Andrews, PhD
SUNY Buffalo, Department of Biostatistics
242 Farber Hall, candrews at buffalo.edu, 716 829 2756