come by vs drop in

come by

verb
  • To come near to; to pass; to visit. 

  • To obtain; to get, especially by chance or involuntarily. 

intj
  • A command to a sheepdog to move clockwise around the sheep 

drop in

verb
  • To arrive casually and unannounced, with little or no warning; also, to visit without an appointment. 

  • To paddle into and take off on a wave another surfer is already riding. 

How often have the words come by and drop in occurred in a corpus of books? (source: Google Ngram Viewer )