[R] converting a factor in numeric values with direct control of the numeric values

[Charles C. Berry]

On Sat, 17 Jan 2009, Jörg Groß wrote:

> Hi,
>
> I know how to convert a factor-variable into a numeric variable via 
> as.numeric().
>
> But how can I control the values that are assigned?
>
>
> For example, I have this factor-variable:
>
>
> z <- c("male", "male", "female")
> z <- as.factor(z)
>
>
> And I want to convert male in 3 and female into the numeric value 5 (just for 
> the example)
>
> so that I get:
>
> [1] 3 3 5


Like this:
> z <- c("male", "male", "female")
> z <- as.factor(z)
> num.codes[ levels(z) ][ z ]
   male   male female
      3      3      5
>
or if you want to avoid the names():

> z.to.num <- unname(num.codes)[ match(levels(z),names(num.codes)) ]
> z.to.num[ z ]
[1] 3 3 5
>


See

 	?as.character
 	?match
 	?levels

HTH,

Chuck

>
>
> Thanks for any help!
>
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Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901