title: How do I add numbers to a column based on another column? (dictionary)
body: <p>I have a dictionary with values that I need to add to a column in a dataframe. The dictionary looks like this:</p>
  
  <pre><code>{1:123, 2:345, 3:678}
  </code></pre>
  
  <p>and the column of the dataframe looks like this:</p>
  
  <pre><code>col1 
  1     
  2
  3
  
  </code></pre>
  
  <p>and I want this result:</p>
  
  <pre><code>col1
  1123
  2345
  3678
  </code></pre>
  
  <p>This is code I am using (replace function)</p>
  
  <pre><code>file['col1'] = file['col1'].replace(dict)
  
  </code></pre>
  
  <p>but replace() unfortunately deletes the value in column 1.</p>