R help - May 2002 - coercing "numeric" components of data frame to "factor" or "ordered"?

I am getting ready to load a bunch of data into R.  The data is all
numeric, but some of the numbers are integer codes representing
non-numeric semantics.  What is the best way to "fix" the data frames
so that these compenents are recognized as "factors" or
"ordered", as
appropriate?

Can I "assign" to some attribute of the data frame component, like the
"class" or "levels" to get the desired effect?

Thanks!

-- 
Russell Senior         ``The two chiefs turned to each other.        
seniorr at aracnet.com      Bellison uncorked a flood of horrible       
                         profanity, which, translated meant, `This is
                         extremely unusual.' ''
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I am not sure if this is the best way, but one way to do this is simply to
call the as.factor function.  Here is a trivial example.
> x <- c(1, 1, 2, 2, 2, 4, 5, 5)
> y <- rnorm(length(x))
> dd <- data.frame(x, y)
> dd$x <- as.factor(dd$x)
Now the x component is a factor.

Cheers,

Andy

__________________________________
Andy Jaworski
Engineering Systems Technology Center
3M Center, 518-1-01
St. Paul, MN 55144-1000
-----
E-mail: apjaworski at mmm.com
Tel:  (651) 733-6092
Fax:  (651) 736-3122



                    Russell Senior
                    <seniorr at aracne      To:     r-help at
stat.math.ethz.ch
                    t.com>               cc:     (bcc: Andrzej P.
Jaworski/US-Corporate/3M/US)
                                         Subject:     [R] coercing
"numeric" components of data frame to "factor" or
"ordered"?
                    05/02/2002
                    16:45








I am getting ready to load a bunch of data into R.  The data is all
numeric, but some of the numbers are integer codes representing
non-numeric semantics.  What is the best way to "fix" the data frames
so that these compenents are recognized as "factors" or
"ordered", as
appropriate?

Can I "assign" to some attribute of the data frame component, like the
"class" or "levels" to get the desired effect?

Thanks!

--
Russell Senior         ``The two chiefs turned to each other.
seniorr at aracnet.com      Bellison uncorked a flood of horrible
                         profanity, which, translated meant, `This is
                         extremely unusual.' ''
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
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Dear Russell,

At 02:45 PM 5/2/2002 -0700, you wrote:
>I am getting ready to load a bunch of data into R.  The data is all
>numeric, but some of the numbers are integer codes representing
>non-numeric semantics.  What is the best way to "fix" the data
frames
>so that these compenents are recognized as "factors" or
"ordered", as
>appropriate?
>
>Can I "assign" to some attribute of the data frame component, like
the
>"class" or "levels" to get the desired effect?
>
>Thanks!

Actually, you can do exactly what you suggest. Say you have a data frame df 
with numeric variables one and two:

         attr(df$one, 'levels') <- sort(unique(df$one))
         class(df$one) <- 'factor'

         attr(df$two, 'levels') <- sort(unique(df$two))
         class(df$two) <- c('ordered', 'factor')

But it's probably simpler just to do

         df$one <- factor(df$one)
         df$two <- ordered(df$two)

I hope that this helps,
  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
-----------------------------------------------------

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