title: add static string to each element in a PANDAs column with multiple strings
body: <p>I have some content that looks like this in a dataframe, 'df'.</p>
  
  <p><code>**column_name**    **data_type**
  data            action , is_enabled , is_system , name , packa...
  data            buckets availableBytes , totalBytes , utc
  data            discharge
  data            buckets failures , hour , success
  data            country , dnssuffix , store</code></p>
  
  <p>I'd like to have a new column where I can attach 'data.' string to each element in the comma separated strings, in df['data_type']. 
  So, for instance in the first row, I'd have a new column based off df['data_type'], named df['elements']. It would contain values </p>
  
  <pre><code>data.action, data.is_enabled, data.is_system, data.name, 
  </code></pre>
  
  <p>etc...</p>
  
  <p>I'm having difficulty creating this new column? With the code below.</p>
  
  <pre><code>df['elements'] = ['data' + s for s in df['data_type']]
  </code></pre>