R help - Nov 2003 - as.double( factor(something) )??

It's in the FAQ, Q7.12.

On Wed, 19 Nov 2003, RenE J.V. Bertin wrote:
> After converting a numeric variable into a factor, is there a way to
convert it back to the original values? as.double() doesn't do that
correctly, for evident reasons (I guess) and as shown below.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

Have you considered the following: 

      > f <- factor(1:2)
      > as.numeric(as.character(f))
      [1] 1 2

      See Venables and Ripley (2000) S Programming (Springer, p. 15). 

      Is this what you want?  spencer graves

RenE J.V. Bertin wrote:
>Hello,
>
>After converting a numeric variable into a factor, is there a way to convert
it back to the original values? as.double() doesn't do that correctly, for
evident reasons (I guess) and as shown below.
>
>Thanks,
>RenE Bertin
>
>  
>
>>dd<-c( rep(0,10), rep(1,10) )
>>dd
>>    
>>
> [1] 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1
>  
>
>>as.double(dd)
>>    
>>
> [1] 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1
>  
>
>>dd<-factor(dd)
>>dd
>>    
>>
> [1] 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1
>Levels: 0 1
>  
>
>>as.double(dd)
>>    
>>
> [1] 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2
>  
>
>>dd<-c( rep(1,10), rep(0,10) )
>>as.double(dd)
>>    
>>
> [1] 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0
>  
>
>>dd<-factor(dd)
>>dd
>>    
>>
> [1] 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0
>Levels: 0 1
>  
>
>>as.double(dd)
>>    
>>
> [1] 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
>  
>
>>as.double(ordered(dd))
>>    
>>
> [1] 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
>  
>
>>dd<-c( rep(1,10), rep(0,10), rep(-2,10) )
>>dd
>>    
>>
> [1]  1  1  1  1  1  1  1  1  1  1  0  0  0  0  0  0  0  0  0  0 -2 -2 -2 -2
-2 -2 -2 -2 -2 -2
>  
>
>>as.double(dd)
>>    
>>
> [1]  1  1  1  1  1  1  1  1  1  1  0  0  0  0  0  0  0  0  0  0 -2 -2 -2 -2
-2 -2 -2 -2 -2 -2
>  
>
>>dd<-factor(dd)
>>dd
>>    
>>
> [1] 1  1  1  1  1  1  1  1  1  1  0  0  0  0  0  0  0  0  0  0  -2 -2 -2 -2
-2 -2 -2 -2 -2 -2
>Levels: -2 0 1
>  
>
>>as.double(dd)
>>    
>>
> [1] 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
>
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>  
>

On Wed, 19 Nov 2003, Spencer Graves wrote:
>       Have you considered the following:
>
>       > f <- factor(1:2)
>       > as.numeric(as.character(f))
>       [1] 1 2
>
>       See Venables and Ripley (2000) S Programming (Springer, p. 15).
Or see the FAQ, which makes the same point.

	-thomas