title: convert multiple json objects to pandas dataframe
body: <p>I am new to python and having trouble with something that seems conceptually very simple. I've read a number of SO posts but still can't solve my problem(s).</p>
  
  <p>I have a function to convert amazon reviews to json format. Each review becomes a single json object. I would like to compile all reviews in a single dataframe, with the json keys as columns and each review in a row.</p>
  
  <p>There are a large number of reviews, each formatted like so:</p>
  
  <pre><code>{
  "product/productId": "B00006HAXW",
  "product/title": "Winnie the Pooh",
  "product/price": "unknown",
  "review/userId": "A1RSDE90N6RSZF",
  "review/profileName": "piglet",
  "review/helpfulness": "9/9",
  "review/score": "5.0",
  "review/time": "1042502400",
  "review/summary": "Love this book", 
  "review/text" : "Exciting stories about highly intelligent creatures, very inspiring!"
  }
  </code></pre>
  
  <p>How can I compile all reviews into a pandas dataframe? I'm having two separate problems:</p>
  
  <ol>
  <li><p>How do I compile all reviews in one object? Currently, the output is generated like so:</p>
  
  <pre><code>for e in parse("reviews.txt.gz"):
      print json.dumps(e)
  </code></pre></li>
  </ol>
  
  <p>I tried creating an empty <code>list</code> and using <code>append</code>:</p>
  
  <pre><code>    for e in parse("reviews.txt.gz"):
          revs = []
          revs = revs.append(json.dumps(e))
  </code></pre>
  
  <p>but that does not work - <code>print revs</code> prints out </p>
  
  <pre><code>None
  None
  None 
  </code></pre>
  
  <ol start="2">
  <li>When I use <code>pd.read_json</code> on a single review formatted as above, it returns "If using all scalar values, you must must pass an index".  Does this mean I do not have valid json format data?</li>
  </ol>