title: Python pandas: labeling categorical values based on legend dataframe
body: <p>I have a big dataset (2m rows, 70 variables), which has many categorical variables. All categorical variables are coded in numbers (e.g. see df1)</p>
  
  <pre><code>df1:
     obs  gender  job
      1     1       1
      2     1       2
      3     2       2
      4     1       1
  </code></pre>
  
  <p>I have a another data frame with all explanations, looking like this: </p>
  
  <pre><code>df2:
  Var:     Value:   Label:
  gender     1      male
  gender     2      female
  job        1      blue collar
  job        2      white collar
  </code></pre>
  
  <p>Is there a fast way to replace all values of the categorical columns with their label from df2? This would save me the work to always look up the meaning of the value in df2. I found some solutions to replace values by hand, but I look for an automatic way doing this. </p>
  
  <p>Thank you</p>