[R] converting factor to numeric

kjetil brinchmann halvorsen kjetil at entelnet.bo
Fri Aug 22 02:40:28 CEST 2003


The R FAQ says: 

7.12 How do I convert factors to numeric?

It may happen that when reading numeric data into R (usually, when 
reading in a file), they come in as factors. If f is such a factor 
object, you can use


to get the numbers back. More efficient, but harder to remember, is


In any case, do not call as.numeric() or their likes directly. 

But trying to follow the advice:

(this is without package method attached, but the results are the 
same with):

First doing as one shouldn't:

> table( as.numeric(EdadC) )

  1   2   3   4   5 
 20  99 157 127  74 

Doing as the FAQ says:

> table( as.numeric(as.character(EdadC)) )
Warning message: 
NAs introduced by coercion 


> table( as.numeric(levels(EdadC))[as.integer(EdadC)] )
Warning message: 
NAs introduced by coercion 


Kjetil Halvorsen

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