title: Count hashtag frequency in a dataframe
body: <p>I am trying to count the frequency of hashtag words in the 'text' column of my dataframe.</p>
  <pre><code>index        text
  1            ello ello ello ello #hello #ello
  2            red green blue black #colours
  3            Season greetings #hello #goodbye 
  4            morning #goodMorning #hello
  5            my favourite animal #dog
  
  </code></pre>
  <pre><code>word_freq = df.text.str.split(expand=True).stack().value_counts()
  </code></pre>
  <p>The above code will perform a frequency count on all strings in the text column, but I just to return the hashtag frequencies.</p>
  <p>For example after running the code on my dataframe above, it should return</p>
  <pre><code>#hello        3
  #goodbye      1
  #goodMorning  1
  #ello         1
  #colours      1
  #dog          1
  </code></pre>
  <p>Is there a way of slightly re-jigging my word_freq code so it only counts hashtag words and returns them in the way I put above? Thanks in advance.</p>