title: Python - ValueError: Cannot index with vector containing NA / NaN values
body: <p>I'm trying to get the average price of products containing any substrings from a wordlist from a dataframe. I've been able to do so with the following code on multiple spreadsheets - </p>
  
  <pre><code>dframe['Product'].fillna('', inplace=True)
  dframe['Price'].fillna(0, inplace=True)
  total_count = 0
  total_price = 0
  for word in ransomware_wordlist:
      mask = dframe.Product.str.contains(word, case=False)
      total_count += mask.sum()
      total_price += dframe.loc[mask, 'Price'].sum()
  average_price = total_price / total_count
  print(average_price)
  </code></pre>
  
  <p>However, one of the spreadsheets throws an error at line -</p>
  
  <pre><code>dframe['Product'].fillna('', inplace=True)
  </code></pre>
  
  <p>with</p>
  
  <pre><code>ValueError: cannot index with vector containing NA / NaN values
  </code></pre>
  
  <p>I fail to understand why <code>dframe['Product'].fillna('', inplace=True)</code> isn't handling this problem.</p>
  
  <p>In desperate need of some help! Thanks!</p>