ddf-project/DDF — pull request #30 by ljzzju (2014-11-07 10:23:43+00:00)
Title: Fix head bug

when the ddf contains only one column, there exits errors:

Error in paste("as", type, sep = ".") :
cannot coerce type 'closure' to vector of type 'character'

ADD dataFrame method to choose selected columns as R dataFrame.