Is there a vectorized way to use is.numeric?

Question

I was reading this question at SO and was wondering if there is any way to use is.numeric in a vectorized way. The point being, if you have a vectorized way to check if a variable is numeric, then any function what depends on the variable being numeric can be vectorized. Otherwise, it cannot be vectorized.

Answer 1

As per the comments:

if you're looking to test columns of a data.frame with as.numeric, use apply

> dat <- data.frame(v1=1:5,v2=letters[1:5],v3=rnorm(5),v4=c(1,2,'c','d',5))

> sapply(dat,is.numeric)
   v1    v2    v3    v4 
 TRUE FALSE  TRUE FALSE 

Or, for variety, you can use colwise from the plyr package:

> colwise(is.numeric)(dat)
    v1    v2   v3    v4
1 TRUE FALSE TRUE FALSE