-----Original Message-----
From: Achim Zeileis [mailto:Achim.Zeileis at wu-wien.ac.at]
Sent: Wednesday, April 20, 2005 12:13 PM
To: Ravi Varadhan
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] Keeping factors with zero occurrences in "table" output
On Wed, 20 Apr 2005 11:38:13 -0400 Ravi Varadhan wrote:
Dear R group,
I have a data frame which contains data on preferences on 7 items
(ranks 1 through 7) listed by each participant. I would like to
tabulate this in a 7x7 table where the rows would be the items and the
columns would be the number of times that item received a particular
rank.
I tried doing this by creating a matrix by "rbind"ing each vector
obtained using "table" on each item. This, however, does not work
because there are some items which didn't receive some of the ranks,
so "table" does not list that item. Is there a way to force it to
list the item and give a "0" to it? Or, is there a simpler way to
solve this problem?
I think the cleanest way is to store the preferences as a "factor" and
tell R at the creation of that factor what the levels are, i.e.
preference <- factor(preference, levels = 1:7)
Then calling
table(preference)
will also report categories with 0 observations.
Z
Thanks for any help,
Ravi.
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Ravi Varadhan, Ph.D.
Assistant Professor, The Center on Aging and Health
Division of Geriatric Medicine and Gerontology
Johns Hopkins University
Ph: (410) 502-2619
Fax: (410) 614-9625
Email: <mailto:rvaradhan at jhmi.edu> rvaradhan at jhmi.edu
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