[R] as.numeric() generates NAs inside an apply call, but fine outside of it

[peter dalgaard]

On Jan 9, 2012, at 15:11 , Chris Beeley wrote:

> Hello-
> 
> I have rather a messy SPSS file which I have imported to R, I've dput'd some of the columns at the end of this message. I wish to get rid of all the labels and have numeric values using as.numeric. The funny thing is it works like this:
> 
> as.numeric(mydata[,2]) # generates correct numbers
> 
> however, if I pass the whole dataframe at once like this:
> 
> apply(mydata, 1:2, function(x) as.numeric(x))


This is your problem. apply(mydata,....) implies as.matrix(mydata) and that turns everything to character, and in the case of a factor column that means the _levels_. I.e., this effect:

> as.matrix(mydata)
      id   item2.jan11    item12.jan11
 [1,] " 1" "quite a lot"  "  5"       
 [2,] " 2" "somewhat"     "  5"       
 [3,] " 3" "missing data" "999"       
 [4,] " 4" "quite a lot"  "  5"       
....

You might be looking for 

as.data.frame(lapply(mydata, as.numeric))



-- 
Peter Dalgaard, Professor
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com