title: filtering the tag set and make the sequence of bigram
body: <p>I'm sorry to ask question with same text file.
  below is my working text file string.</p>
  
  <pre><code>The/at Fulton/np-tl County/nn-tl Grand/jj-tl Jury/nn-tl said/vbd Friday/nr an/at investigation/nn of/in Atlanta's/np$ recent/jj primary/nn election/nn produced/vbd
  </code></pre>
  
  <p>This string consists of the <code>"word / its tag"</code> format, as you can see. From this string, I want to filter only the sequence of <code>"noun + adjective"</code> and make them to the bigram. For example, <code>"Grand/jj-tl Jury/nn-tl"</code> is exact word sequence that I want. (<code>nn</code> means noun, <code>jj</code> means adjective and adjuncts such as <code>"-tl"</code> are additional information about the tag.) </p>
  
  <p>Maybe this will be easy job. And I first used regex for filtering. Below is my code.</p>
  
  <pre><code>import re
  f = open(textfile)
  raw = f.read()
  tag_list = re.findall("\w+/jj-?\w* \w+/nn-?\w*", raw)
  print tag_list 
  </code></pre>
  
  <p>This codes give me the exact words list. However, what I want is the bigram data. That code only gives me the list of words, such like this. </p>
  
  <pre><code>['Grand/jj-tl Jury/nn-tl', 'recent/jj primary/nn', 'Executive/jj-tl Committee/nn-tl']
  </code></pre>
  
  <p>I want this data to be converted such as below.</p>
  
  <pre><code>[('Grand/jj-tl, Jury/nn-tl'), ('recent/jj ,primary/nn'), ('Executive/jj-tl , Committee/nn-tl')]
  </code></pre>
  
  <p>i.e. the list of bigram data. I need your advice.</p>