title: pandas df merge avoid duplicate column names
body: <p>The question is when <code>merge</code> two <code>df</code>s, and they all have a column called <code>A</code>, then the result will be a df having <code>A_x</code> and <code>A_y</code>, I am wondering how to keep <code>A</code> from one <code>df</code> and discard another one, so that I don't have to rename <code>A_x</code> to <code>A</code> later on after the merge.</p>