thr3ads.net - R help - [R] Newbie struggling with "factors" [Mar 2002]

If this information is useful, please help other people find it:
Share via:

Tom Arnold

2002-Mar-29 13:58 UTC

[R] Newbie struggling with "factors"

I am processing some survey results, and my data are
being read in as "factors". I don't know how to
process these things in any way.

To start with, several of the survey questions are
mulit-choice check boxes on the original (web-based)
survey, as in "check all that apply".

These are encoded as numbers. For example, if the
survey has a question:
Which operating systems have you used? (Check all that
apply)
[ ]Windows
[ ]Macinotsh
[ ]Unix

...then the data exported for three different
responses might look like
;1;
;1,3;
;1,2,3;

...where ";" is the field delimiter. 
I use read.table to get the data in. I read all the
survey data into a table "n" and the field above is
called "OSUSE". When I query R about the field, it
tells me it is class "factor"
> class(n$OSUSE)
[1] "factor"> mode(n$OSUSE)[1] "numeric"

I'd like to be able to do some simple things like:
what is the most common item checked (1, 2, or 3?)
What is the average number of boxes checked?

But I can't find any way to manipulate this "factor"
field. What's the secret?

Thanks.

====Tom Arnold
Summit Media Partners
Visit our web site at http://www.summitmediapartners.com

__________________________________________________

Yahoo! Greetings - send holiday greetings for Easter, Passover

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Jonathan Baron

2002-Mar-29 15:10 UTC

head link

[R] Newbie struggling with "factors"

On 03/29/02 05:58, Tom Arnold wrote:>I am processing some survey results, and my data are
>being read in as "factors". I don't know how to
>process these things in any way.
You can convert them to numbers with as.numeric(), but that
doesn't seem to be your immediate problem.  Factors are like what
some other programs call "categorical variables."  They ordering
doesn't mean anything.  They are just labels.  Sometimes that
_is_ exactly what you want.

You can also use various options on read.table() to control how
things are coded.  (See the help on it.)  But that doesn't seem
to be your problem either.
>To start with, several of the survey questions are
>mulit-choice check boxes on the original (web-based)
>survey, as in "check all that apply".
>
>These are encoded as numbers. For example, if the
>survey has a question:
>Which operating systems have you used? (Check all that
>apply)
>[ ]Windows
>[ ]Macinotsh
>[ ]Unix
>
>...then the data exported for three different
>responses might look like
>;1;
>;1,3;
>;1,2,3;
>...where ";" is the field delimiter. 
I assue you have told read.table() that ";" is the delimiter,
with the appropriate option setting.  But this would mean, I
think, that you would have some fields that look like "1,2,3".
This is probably why you are getting factors: "1,2,3" is not a
number, so R assumes it is part of a factor.  To extract the
numbers from things like this, you might have to use things like
substr() and strsplit().
>I use read.table to get the data in. I read all the
>survey data into a table "n" and the field above is
>called "OSUSE". When I query R about the field, it
>tells me it is class "factor"
>
>> class(n$OSUSE)
>[1] "factor"
>> mode(n$OSUSE)
>[1] "numeric"
I'm surprised at this.  I would think it would be character.
>I'd like to be able to do some simple things like:
>what is the most common item checked (1, 2, or 3?)
>What is the average number of boxes checked?
>
>But I can't find any way to manipulate this "factor"
>field. What's the secret?
Using the various string manipulation commands, possibly also
with apply() or loops.

But, more generally, you might rethink the way you do your
questionnaires or have your data reported.  I do this kind of
research, and I try to avoid checkboxes or select boxes for just
this reason.  (I tend to use buttons and then write JavaScript
code to read the buttons and turn their results into something
nice and regular.)  Time saved in writing the web page is lost
when you try to analyze the data.  You might also try various
pre-processing of your data.

In particular, what you might aim for is to have a data file for
each respondent with all commas or all semicolon.  A response
like "1,2" would be represented as "1,2,0".  That is, you
would
pad the data to fill up the right number of fields.

Now, again, you can, if you want, handle all this with string
manipulation in R, and perhaps you can develop general tools that
you can use over and over.  But, if you are just starting, you
might consider the alternatives too.
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

John Fox

2002-Mar-29 18:24 UTC

head link

[R] Newbie struggling with "factors"

Dear Jonathan and Tom,

At 10:10 AM 3/29/2002 -0500, Jonathan Baron wrote:>On 03/29/02 05:58, Tom Arnold wrote:
>
> >When I query R about the field, it
> >tells me it is class "factor"
> >
> >> class(n$OSUSE)
> >[1] "factor"
> >> mode(n$OSUSE)
> >[1] "numeric"
>
>I'm surprised at this.  I would think it would be character.
Factors are numeric vectors of class factor, with the level information 
given by a levels attribute; for example:

     > fac <- factor(rep(c("a", "b"), 2))
     > fac
     [1] a b a b
     Levels:  a b

     > unclass(fac)
     [1] 1 2 1 2
     attr(,"levels")
     [1] "a" "b"

     > class(fac)
     [1] "factor"

     > mode(fac)
     [1] "numeric"
     >

Regards,
  John
-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox
-----------------------------------------------------

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Tom Arnold

2002-Mar-29 22:17 UTC

head link

[R] Newbie struggling with "factors"

To all who have offered suggestions: 
THANKS! Wow, this list has generated a lot of good
ideas for me in a very short time, and I appreciate
it.

For now, I've got some solutions to my problem. Greg's
suggestion about creating a subclass to handle the
"multi-checkbox" type of question is probably the most
flexible, in the long run. However, I've not chosen it
in the short run because my programming experience is
deeper in the procedural vein than in OOP. I'm only
just starting to see how the OO qualities of R can be
used, and I'm not yet comfortable in coding that way.

Following the suggestions of several people on the
list, I have created a few functions that proceed this
way for my multi-choice questions:
- create a matrix with as many rows as there are
responses, and as many columns as there are
"checkboxes" in the original question

- use strsplit to break up the factors based on the
separator inside the field

- for each column in the matrix that I created, fill
it with T/F (1/0) by using the is.element function to
determine which responses had each checkbox checked

- use the resulting matrix to create whatever sums,
averages and plots I want

The code I wrote is not pretty, but is working for me
at the moment. I'm an old assembly and C programmer
mainly, so I'm still getting used to the capabilities
and idioms of R. I think my code does great violence
to both and probably makes the interpreter thrash
pitifully, but for now it seems to produce the correct
result and I can understand it! I'll look for elegance
as I go along.
--- "Warnes, Gregory R"
<gregory_r_warnes at groton.pfizer.com> wrote:> 
> Hint #1,  to do any useful transformations on your
> variables you will
> probably need to convert them temporarily into
> character variables (aka
> strings).  Do that with 
> 
> 	as.character(n$OSUSE)
> 
> Probably your will want to convert each of the
> variables that are in this
> format into a set of numeric variables.  Something
> like this:
> 
> 	n <- data.frame(OSUSE =
c("1","1,3","1,2,3"))
> 	n$OSUSE.Windows   <- sapply( strsplit(n$OSUSE, ",")
> , function(X) (
> "1" %in% X ) )
> 	n$OSUSE.Macintosh <- sapply( strsplit(n$OSUSE, ",")
> , function(X) (
> "2" %in% X ) )
>      	n$OSUSE.Unix      <- sapply( strsplit(n$OSUSE,
> ",") , function(X) (
> "3" %in% X ) )
> 
> Alternatively, if you often have variables like
> this, you might consider
> creating a new object type that extends factor and
> that includes the
> operations that you need.  
> 
> Something like:
> 
> ### Start Sample Code ###
> 
> checklist <- function(X, boxnames)
>   {
>     attr(X, "boxnames") <- boxnames
>     class(X) <- c("checklist","factor")
>     return(X)
>   }
> 
> contains <- function(X, name)
>   {
>     if(is.character(name) )
>       name <- pmatch( name, attr(X,"boxnames" ) )
>                      
>     retval <- sapply( strsplit(X, ",") , function(X)
> ( name %in% X ) )
>     return(retval)
>   }
> 
> numchecked <- function(X)
>   {
>     retval <- sapply( strsplit(X, ","), length )
>     return(retval)
>   }
> 
> summary.checklist <- function(x, ...)
>   {
>     sum <- apply( as.matrix(x), 2, sum )
>     mean <- apply( as.matrix(x), 2, mean )
>     return( rbind(sum,mean))
>   }
> 
> as.matrix.checklist <- function(x, ...)
>   {
>     sapply( attr(x, "boxnames"), function(YY)
> contains(x, YY) )
>   }
> 
> ### End Sample Code ##
> 
> Here's some examples of using these functions:
> 
> > n <- data.frame(OSUSE =
c("1","1,3","1,2,3"))
> > 
> > n$OSUSE <- checklist(n$OSUSE,
> c("Windows","Macintosh","Unix"))
> #
> # Check if OSUSE includes a specific OS
> #
> > contains( n$OSUSE, "Windows")
> [1] TRUE TRUE TRUE
> > contains( n$OSUSE, "Macintosh")
> [1] FALSE FALSE  TRUE
> > contains( n$OSUSE, "Unix")
> [1] FALSE  TRUE  TRUE
> >
> #
> # Compute the average number of checked items
> # 
> > numchecked(n$OSUSE)
> [1] 1 2 3
> > mean(numchecked(n$OSUSE))
> [1] 2
> > 
> #
> # Create a matrix showing whether each box was
> checked or not
> #
> > as.matrix(n$OSUSE)
>      Windows Macintosh  Unix
> [1,]    TRUE     FALSE FALSE
> [2,]    TRUE     FALSE  TRUE
> [3,]    TRUE      TRUE  TRUE
> > 
> #
> # Show some summary info
> #
> > summary(n$OSUSE)
>      Windows Macintosh      Unix
> sum        3 1.0000000 2.0000000
> mean       1 0.3333333 0.6666667		
> 
> 
> Of course, you'll want to modify these classes to
> suit your needs.  A little
> time up front can help a lot.
> 
> If you like, I'll include these classes and any
> enhancements that you make
> in my 'gregmisc' library.
> 
> 
> -Greg
> 
> 
> > -----Original Message-----
> > From: Tom Arnold
> [mailto:thomas_l_arnold at yahoo.com]
> > Sent: Friday, March 29, 2002 8:59 AM
> > To: R
> > Subject: [R] Newbie struggling with "factors"
> > 
> > 
> > I am processing some survey results, and my data
> are
> > being read in as "factors". I don't know how to
> > process these things in any way.
> > 
> > To start with, several of the survey questions are
> > mulit-choice check boxes on the original
> (web-based)
> > survey, as in "check all that apply".
> > 
> > These are encoded as numbers. For example, if the
> > survey has a question:
> > Which operating systems have you used? (Check all
> that
> > apply)
> > [ ]Windows
> > [ ]Macinotsh
> > [ ]Unix
> > 
> > ...then the data exported for three different
> > responses might look like
> > ;1;
> > ;1,3;
> > ;1,2,3;
> > 
> > ...where ";" is the field delimiter. 
> > I use read.table to get the data in. I read all
> the
> > survey data into a table "n" and the field above
> is
> > called "OSUSE". When I query R about the field, it
> > tells me it is class "factor"
> > 
> > > class(n$OSUSE)
> > [1] "factor"
> > > mode(n$OSUSE)
> > [1] "numeric"
> > 
> > I'd like to be able to do some simple things like:
> > what is the most common item checked (1, 2, or 3?)
> > What is the average number of boxes checked?
> > 
> > But I can't find any way to manipulate this
> "factor"
> > field. What's the secret?
> > 
> > Thanks.
> > 
> > ====> > Tom Arnold
> > Summit Media Partners
> > Visit our web site at
> http://www.summitmediapartners.com
> > 
> > __________________________________________________
> > 
> > Yahoo! Greetings - send holiday greetings for
> Easter, Passover
> > 
> >
>
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.> > -.-.-.-.-.-.-.-.-
> > r-help mailing list -- Read 
> > http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
> > Send "info", "help", or "[un]subscribe"
> === message truncated ==

====Tom Arnold
Summit Media Partners
Visit our web site at http://www.summitmediapartners.com

__________________________________________________

Yahoo! Greetings - send holiday greetings for Easter, Passover

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Apparently Analagous Threads

Search for more apparently analagous threads

R help - Mar 2002 - Newbie struggling with "factors"

[R] Newbie struggling with "factors"

[R] Newbie struggling with "factors"

[R] Newbie struggling with "factors"

[R] Newbie struggling with "factors"

Apparently Analagous Threads