merge vs play by ear

merge

verb
  • To blend gradually into something else. 

  • To combine into a whole. 

noun
  • The joining together of multiple sources. 

play by ear

verb
  • To do by guessing, intuition, or trial and error; to react to events as they occur; improvise 

  • To play guided by one's musical ear, rather than from a written score. 

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