title: How to separate a numpy array into separate columns in pandas
body: <p>I have a dataframe that looks like</p>
  
  <pre><code>  ID_0 ID_1  ID_2
  0    a    b  0.05
  1    a    b  0.10
  2    a    b  0.19
  3    a    c  0.25
  4    a    c  0.40
  5    a    c  0.65
  6    a    c  0.71
  7    d    c  0.95
  8    d    c  1.00
  </code></pre>
  
  <p>I want to groupby and make a normalized histogram of the ID_2 column for each group. So I do</p>
  
  <pre><code>df.groupby(['ID_0', 'ID_1']).apply(lambda x: np.histogram(x['ID_2'], range = (0,1), density=True)[0]).reset_index(name='ID_2')
  </code></pre>
  
  <p>However what I would really like is for the 11 elements of the numpy arrays to be in separate columns  of the dataframe.  </p>
  
  <p>How can I do this?</p>