title: Why am I getting this error about "string indices must be integer"?
body: <p>I am looking to find the total number of players by counting the unique screen names. 
      # Dependencies
      import pandas as pd</p>
  
  <pre><code># Save path to data set in a variable
  df = "purchase_data.json"
  
  # Use Pandas to read data
  data_file_pd = pd.read_json(df)
  data_file_pd.head()
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/z6WMP.png" alt="enter image description here"></p>
  
  <pre><code># Find total numbers of players
  player_count = len(df['SN'].unique())
  
  TypeError                                 Traceback (most recent call last)
  &lt;ipython-input-26-94bf0ee04d7b&gt; in &lt;module&gt;()
    1 # Find total numbers of players
  ----&gt; 2 player_count = len(df['SN'].unique())
  
  TypeError: string indices must be integers
  </code></pre>