converting a factor in numeric values with direct control of the numeric values

On Sat, 17 Jan 2009, J?rg Gro? 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 <- c(male = 3, female = 5 )

 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!

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