title: How to set row value in pandas dataframe?
body: <p>I need to set the first row's value of a column for every group to False.</p>
  <p><code>        start_ix = group.head(1).index</code></p>
  <p><code>        print(start_ix)</code></p>
  <blockquote>
  <p>Int64Index([20], dtype='int64')</p>
  </blockquote>
  <p><code>        print df.iloc[start_ix]['start']</code></p>
  <blockquote>
  <p>20    False</p>
  <p>Name: start, dtype: bool</p>
  </blockquote>
  <p><code>        df.iloc[start_ix]['start'] = True</code></p>
  <p>But the value stays <code>False</code> upon inspecting the DataFrame.</p>