apply(iris,2,function(x) class(x))
 #  Sepal.Length  Sepal.Width Petal.Length  Petal.Width      Species
 # "character"  "character"  "character"  "character"  "character"

apply(iris[,1:4],2,function(x) class(x))
#  Sepal.Length  Sepal.Width Petal.Length  Petal.Width
#  "numeric"    "numeric"    "numeric"    "numeric"