title: Remap values in a dataframe where the key is one column and the value to be replaced is another column
body: <p>I have a dictionary which is a mapping of id's to correct names for a company.
  say the dict is <code>correct_names = {1: 'fixed_name', 2:'fixed_name1}</code></p>
  
  <p>I would like to apply it to a dataframe similar to:</p>
  
  <pre><code>        ID     name_col
  0       1      name
  1       2      name1
  2       3      name2
  3       4      name3
  </code></pre>
  
  <p>So it goes in and fixes all the bad company names.</p>
  
  <pre><code>        ID     name_col
  0       1      fixed_name
  1       2      name1
  2       3      fixed_name1
  3       4      name3
  </code></pre>