title: Using if-condition in pandas to fill na values in pandas
body: <p>I have some columns in df where one of the columns has a missing value. I need to fill them but only when the ColumnY has a False value.</p>
  <p>Here is how df looks</p>
  <pre><code>A                 B                    C
  Value             4                    True
  v3                9                    True
  v9                                     False
  v0                4                    False
  </code></pre>
  <p>I have a dictionary which I am using to map the values in column B ...</p>
  <pre><code>di_map = {'V3' : 'A',  'V9' : 'X', 'V0' : 'Z'  }
  
  
  
  df['B'] =  df['A'].map(di_map)
  </code></pre>
  <p>Here is how output should look</p>
  <pre><code>A                 B                    C
  Value             4                    True
  v3                9                    True
  v9                X                    False
  v0                Z                    False
  </code></pre>