title: Pandas: column present in one df and not in the other
body: <p>I have two data frames A and B with columns, [a,b,c] and [c,d,f] respectively. I want to select the column 'a' from data-frame A, such that the elements of column 'c' are present in A, but not in B. How would I got about it?</p>
  
  <p>Something like the sql equivalent of, 'Select a from A such that c in A and c not in B'</p>
  
  <p>Thanks!</p>