title: Extract and count hashtags from a dataframe
body: <p>I have a dataframe with some tweets, something like this:</p>
  
  <pre><code>tweets = pd.Series(['This is a tweet example #help #thankyou', 
                      'Second tweet example #help', 
                      'Third tweet example #help #stackoverflow'])
  
  tweets_df = pd.DataFrame({'Tweets': tweets})
  </code></pre>
  
  <p>Then I put the hashtags in another column of the dataframe</p>
  
  <pre><code>tweets_df['hashtags'] = tweets_df['Tweets'].apply(lambda twt : re.findall(r"#(\w+)", twt))
  </code></pre>
  
  <p>Now I want to count them and put the results in another dataframe. I have tried with the following but didn't worked</p>
  
  <pre><code>tweets_df['hashtags'].str.split(expand=True).stack().value_counts()
  </code></pre>
  
  <p>The result must be something like:</p>
  
  <pre><code>#help           2
  #thankyou       1
  #stackoverflow  1
  </code></pre>