title: How do I reshape only parts of a dataframe
body: <p>I have a dataframe that looks like this:</p>
  
  <pre><code>         Date       City_State  HousingPrice      DowPrice    NasqPrice
  0     1996-04     New York, NY      169300.0   5579.864351  1135.628092
  1     1996-04  Los Angeles, CA      157700.0   5579.864351  1135.628092
  2     1996-04      Houston, TX       86500.0   5579.864351  1135.628092
  3     1996-04      Chicago, IL      114000.0   5579.864351  1135.628092
  4     1996-04      Phoenix, AZ       88100.0   5579.864351  1135.628092
  5     1996-05     New York, NY      169800.0   5616.707742  1220.540472
  6     1996-05  Los Angeles, CA      157600.0   5616.707742  1220.540472
  </code></pre>
  
  <p>I'm trying to reshape the dataframe so that I could plot it.
  Is there a simple way to move the DowPrice and NasqPrice into the City_State column so it looks something like this, without having to split the dataframe in two, reshape them and then merge them back?</p>
  
  <pre><code>         Date       Category        Price        
  0     1996-04     New York, NY      169300.0   
  1     1996-04  Los Angeles, CA      157700.0   
  2     1996-04      Houston, TX      86500.0   
  3     1996-04      DowPrice         5579.864351   
  4     1996-04      NasqPrice        1135.628092
  
  </code></pre>