title: Replace a value in a column by vlookup another dataframe only if the value exists
body: <p>I want to overwrite my <code>df1.Name</code> values based on a mapping table in <code>(df2.Name1, df2.Name2)</code>. However, not all values in <code>df1.Name</code> exist in <code>df2.Name1</code></p>
  
  <h3>df1:</h3>
  
  <pre><code>Name
  Alex
  Maria 
  Marias
  Pandas
  Coala
  </code></pre>
  
  <h3>df2:</h3>
  
  <pre><code>Name1   Name2
  Alex    Alexs
  Marias  Maria
  Coala   Coalas
  </code></pre>
  
  <h3>Expected Result:</h3>
  
  <pre><code>Name
  Alexs
  Maria
  Maria
  Pandas
  Coalas
  </code></pre>
  
  <p>I have tried several solutions online such as using the Map function. By turning <code>df2</code> in a Dictionary I am using <code>df1.Name = df1.Name.map(Dictionary)</code>, but this will result in <code>nan</code> for all values not in <code>df2</code> as per below.</p>
  
  <pre><code>Name
  Alexs
  Maria
  Maria
  NAN
  Coalas
  </code></pre>
  
  <p>I am not sure how to use an IF statement to replace only the ones that do exist in df2 and keep the rest as per df1.
  I also tried to create a function with <code>if</code> statements, but was big time failure. </p>
  
  <p>How I could approach this problem?</p>