title: Pandas - Convert a column of 1D arrays to a 2D array
body: <p>I have a dataframe with a single column where each row is a 1D array.</p>
  <pre><code>     my_col
  0    [1,2,3,4]
  1    [5,6,7,9]
  2    [8,5,4,3]
  3    [3,6,8,0]
  4    [2,4,6,8]
  </code></pre>
  <p>Where [1,2,3,4], [5,6,7,9], etc. are all 1D arrays of shape (4,). I want to convert this column into an array of 1D arrays. I.e., an array of shape(5,4).</p>
  <p>But, if I try <code>np.array(df['my_col'].values)</code>, the shape I get is (5,). But, how do I get (5,4)?</p>