title: Pandas: assign to column with map
body: <pre><code>import pandas as pd
  df = pd.DataFrame({'a':[&quot;a&quot;,&quot;aa&quot;,&quot;aaaaa&quot;,&quot;a&quot;]})
  df[&quot;len&quot;] = map(len, df[&quot;a&quot;])
  </code></pre>
  <p>Why does this not work? Or rather, why is this not supposed to work?</p>
  <p>I understand that <code>list(map(...))</code> works, and I understand that Pandas would need to provide the functionality to do <code>df[&quot;col&quot;] = map(...)</code></p>
  <p>I wonder more why this was not implemented / why this wouldn't be considered Pythonic / Pandaesque.</p>