title: How can I fill in a missing values in range with Pandas?
body: <p>I have a dataset with a number of values like below.</p>
  
  <pre><code>&gt;&gt;&gt; a.head()
     value  freq
  3      9     1
  2     11     1
  0     12     4
  1     15     2
  </code></pre>
  
  <p>I need to fill in the values between the integers in the value column. For example, I need to insert one new row between 9 &amp; 11 filled with zeroes, then another two between 12-15. The end result should be the dataset with 9-15 with 'missing' rows as zeroes across the board.</p>
  
  <p>Is there anyway to insert a new row at an specific location without replacing data? The only methods I've found involve slicing the dataframe at a location then appending a new row and concatenating the remainder.</p>
  
  <p>UPDATE: The index is completely irrelevant so don't worry about that.</p>