title: How do I perform a math operation on a Python Pandas dataframe column, but only if a certain condition is met?
body: <p>I have a Pandas dataframe that I'm working with and I simply need to divide all values in a certain column that are greater than 800 by 100.  In other words, if the value in the 'credit_score' column is greater than 800, it can be assumed that the data were entered with two extra places to the left of the decimal place.  For example...</p>
  
  <pre><code>id    credit_score    column_b    column_c
  0     750             ...         ...
  1     653             ...         ...
  2     741             ...         ...
  3     65100           ...         ...
  4     73500           ...         ...
  5     565             ...         ...
  6     480             ...         ...
  7     78900           ...         ...
  8     699             ...         ...
  9     71500           ...         ...
  </code></pre>
  
  <p>So I basically want to divide the credit scores for row indexes 3, 4, 7, and 9 by 100, but not the others. I want the new, valid values to replace the old, invalid ones.  Alternatively, a new column such as 'credit_score_fixed' would work too.  I'm fairly new to Python and Pandas, so any help is much appreciated.</p>