title: How do I combine 2 DataFrames and add 2 column values together if both values exist or else return the non-null value instead if one is null?
body: <p>Edit: I've realized that I did not ask my question in the right way. I'm not going to accept one answer over another, but am going to leave all content here for anyone's future use.</p>
  
  <p>I have 2 DataFrames that I want to combine. I'd like to merge them only on the Name column so that all Name values from both DataFrames are included in the resulting DataFrame. I'm having trouble with null values, however. If an Inches value exists in both DataFrames, I'd like to add them together to be a result in df3. If an Inches value only exists in one of the two DataFrames, I'd like the non-null value chosen to be as the df3 Inches value. </p>
  
  <p>ie. 'Silvers' in df1 + 'Silvers' in df2 = 14 for 'Silvers' in df3. Likewise: 'Merole' in df1 + 'Merole' in df2 = 6 for 'Merole' in df3. Or: 'Jones' in df1 + 'Jones' in df2 = 7 for 'Jones' in df3 </p>
  
  <p>I have df1:</p>
  
  <pre><code>Name    | Inches
  ---------------------
  'Silvers'|   7
  'Jones'  |   7
  'Jackson'|   4
  'Merole' |   NaN
  'Kanoff' |   3
  'Walker' |   1
  'Smith'  |   8 
  </code></pre>
  
  <p>And df2:</p>
  
  <pre><code>Name    | Inches
  ---------------------
  'Vickers' |   7
  'Lederman'|   7
  'Silvers' |   7
  'Jones'   |   NaN
  'Merole'  |   6
  'Wilde'   |   2
  'Nichols' |   5
  </code></pre>
  
  <p>I want df3:</p>
  
  <pre><code>Name    | Inches
  ---------------------
  'Vickers' |   7
  'Lederman'|   7
  'Silvers' |   14
  'Jones'   |   7
  'Merole'  |   6
  'Wilde'   |   2
  'Nichols' |   5
  'Jackson' |   4
  'Kanoff'  |   3
  'Walker'  |   1
  'Smith'   |   8 
  </code></pre>
  
  <p>Additionally, how would this be possible if there was a 3rd column with all null values that I want to keep as null?</p>