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

[Robert A LaBudde]

Exactly! Thanks.

At 12:49 AM 6/5/2011, Jorge Ivan Velez wrote:
>Dr. LaBudde,
>
>Perhaps
>
>as.numeric(as.character(x))
>
>is what you are looking for.
>
>HTH,
>Jorge
>
>
>On Sun, Jun 5, 2011 at 12:31 AM, Robert A. LaBudde <> 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: 
><mailto:ral at lcfltd.com>ral at lcfltd.com
>Least Cost Formulations, Ltd.            URL: 
><http://lcfltd.com/>http://lcfltd.com/
>824 Timberlake Drive                     Tel: <tel:757-467-0954>757-467-0954
>Virginia Beach, VA 23464-3239            Fax: <tel:757-467-2947>757-467-2947
>
>"Vere scire est per causas scire"
>
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>

================================================================
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"