title: Date conversion dot to dash (i.e. 2001.01 to 2001-01)
body: <p>I am working with a data set where the Period is given as
  2001.01,2001.02,2001.03......When I am trying to convert it using yearmon() it shows only Jan and Feb this two month.For
  example for 2001.05 it shows Jan 2001. But it should be May 2001. I think I need to convert the Period in 2001-01 format
  first before using yearmon(). Can anyone plz tell me how can I do it?</p>