[R] How to convert a factor column into a numeric one?

[Robert A LaBudde]

Thanks! Exactly what I wanted, as the same as Jorge also suggested.

At 12:49 AM 6/5/2011, Dennis Murphy wrote:
>Hi:
>
>Try this:
>
> > dd <- data.frame(a = factor(rep(1:5, each = 4)),
>+                  b = factor(rep(rep(1:2, each = 2), 5)),
>+                  y = rnorm(20))
> > str(dd)
>'data.frame':   20 obs. of  3 variables:
>  $ a: Factor w/ 5 levels "1","2","3","4",..: 1 1 1 1 2 2 2 2 3 3 ...
>  $ b: Factor w/ 2 levels "1","2": 1 1 2 2 1 1 2 2 1 1 ...
>  $ y: num  0.6396 1.467 1.8403 -0.0915 0.2711 ...
> > de <- within(dd, {
>+          a <- as.numeric(as.character(a))
>+          b <- as.numeric(as.character(b))
>+        } )
> > str(de)
>'data.frame':   20 obs. of  3 variables:
>  $ a: num  1 1 1 1 2 2 2 2 3 3 ...
>  $ b: num  1 1 2 2 1 1 2 2 1 1 ...
>  $ y: num  0.6396 1.467 1.8403 -0.0915 0.2711 ...
>
>
>HTH,
>Dennis
>
>On Sat, Jun 4, 2011 at 9:31 PM, Robert A. LaBudde <ral at lcfltd.com> wrote:
> > I have a data frame:
> >
> >> head(df)
> >  Time Temp Conc Repl    Log10
> > 1    0  -20    H    1 6.406547
> > 2    2  -20    H    1 5.738683
> > 3    7  -20    H    1 5.796394
> > 4   14  -20    H    1 4.413691
> > 5    0    4    H    1 6.406547
> > 7    7    4    H    1 5.705433
> >> str(df)
> > 'data.frame':   177 obs. of  5 variables:
> >  $ Time : Factor w/ 4 levels "0","2","7","14": 1 2 3 4 1 3 4 1 3 4 ...
> >  $ Temp : Factor w/ 4 levels "-20","4","25",..: 1 1 1 1 2 2 2 3 3 3 ...
> >  $ Conc : Factor w/ 3 levels "H","L","M": 1 1 1 1 1 1 1 1 1 1 ...
> >  $ Repl : Factor w/ 5 levels "1","2","3","4",..: 1 1 1 1 1 1 1 1 1 1 ...
> >  $ Log10: num  6.41 5.74 5.8 4.41 6.41 ...
> >> levels(df$Temp)
> > [1] "-20" "4"   "25"  "45"
> >> levels(df$Time)
> > [1] "0"  "2"  "7"  "14"
> >
> > As you can see, "Time" and "Temp" are currently factors, not numeric.
> >
> > I would like to change these columns into numerical ones.
> >
> > df$Time<- as.numeric(df$Time)
> >
> > doesn't work, as it changes to the factor level indices (1,2,3,4) 
> instead of
> > the values (0,2,7,14).
> >
> > There must be a direct way of doing this in R.
> >
> > I tried recode() in 'car':
> >
> >> df$Temp<- recode(df$Temp, '1=-20;2=25;3=4;4=45',as.factor.result=FALSE)
> >> head(df)
> >  Time Temp Conc Repl     Freq
> > 1    0  -20    H    1 6.406547
> > 2    2  -20    H    1 5.738683
> > 3    7  -20    H    1 5.796394
> > 4   14  -20    H    1 4.413691
> > 5    0   45    H    1 6.406547
> > 7    7   45    H    1 5.705433
> >
> > but note that the values for 'Temp' in rows 5 and 7 are 45 and not 4, as
> > expected, although the result is numeric. The same happens if I use the
> > order given by levels(df$Temp) instead of the sort order in the 
> recode() 2nd
> > argument.
> >
> > Any hints?
> > ================================================================
> > Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral at lcfltd.com
> > Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
> > 824 Timberlake Drive                     Tel: 757-467-0954
> > Virginia Beach, VA 23464-3239            Fax: 757-467-2947
> >
> > "Vere scire est per causas scire"
> >
> > ______________________________________________
> > 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.
> >

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral at lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"