[R] Find classes for each column of a data.frame

[Barry Rowlingson]

On Thu, Aug 26, 2010 at 4:44 PM, Marc Schwartz <marc_schwartz at me.com> wrote:

>> sapply(iris, class)
> Sepal.Length  Sepal.Width Petal.Length  Petal.Width      Species
>   "numeric"    "numeric"    "numeric"    "numeric"     "factor"

 Note that comparing the result of class(foo) is a bad way of telling
if something is of a particular class, because of inheritance -
class(foo) can be a vector if the object belongs to more than one
class.

 Always test using is.whatever(foo), which returns TRUE if foo is a whatever:

 > f=factor(letters)
 > class(f)
 [1] "factor"
 > class(f)=c("factor","alphabet")
 > f
  [1] a b c d e f g h i j k l m n o p q r s t u v w x y z
 Levels: a b c d e f g h i j k l m n o p q r s t u v w x y z
 > is.factor(f)
 [1] TRUE

 but now:

 > class(f)=="factor"
 [1]  TRUE FALSE

Barry