title: Pandas Number extraction and replacing in multiple column
body: <p>I am trying to extract number from thounsands of rows and have been using below code,
  I have been able to extract the numbers from the string but unable to replace it in the column.</p>
  <pre><code>df_consol.loc[9122:,'FDD - 1800.1'].head(10)
  </code></pre>
  <p>9122    15 MHz
  9123    15 MHz
  9124    15 MHz
  9125    15 MHz
  9126    15 MHz
  9127    15 MHz
  9128    15 MHz
  9129    15 MHz
  9130    15 MHz
  9131    15 MHz</p>
  <pre><code>New_Col=df_consol['FDD - 1800.1'].str.extract(r'^(\d{2})',expand=False)
  </code></pre>
  <p>OUTPUT
  9122    15
  9123    15
  9124    15
  9125    15
  9126    15
  9127    15
  9128    15
  9129    15
  9130    15
  9131    15</p>
  <pre><code>df_consol['FDD - 1800.1']=df_consol['FDD - 1800.1'].str.extract(r'^(\d{2})',expand=False)
  </code></pre>
  <p>above code is unable to replace the existing columns of the dataframe</p>