title: Setting with copy warning... what am I doing wrong?
body: <p>I've read all kinds of documentation about this warning in Pandas. Aside from getting frustrated because I still haven't seen a case where it's not absolutely clear what is trying to be done (so the warning feels like a needless complication), I'm still getting the warning even when seemingly doing what is recommended.</p>
  <p>Here is my original code. I'm trying to convert two columns ('A' and 'B') to DateTime.</p>
  <p><code>df[['A', 'B']] = df[['A', 'B']].apply(pd.to_datetime)</code></p>
  <p>After reading about using .loc as the preferred method, I changed to:</p>
  <p><code>df.loc[:, ['A', 'B']] = df.loc[:, ['A', 'B']].apply(pd.to_datetime)</code></p>
  <p>But I'm still getting the same warning. Would someone be kind enough to point out what I'm missing?</p>