come by vs drop by

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 by

verb

  • To visit informally and spontaneously. 

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