title: From dict to pandas dataframe
body: <p>I have some code to put nested json dict to dataframe.
  This is not very efficient and wondering if I need to use numpy array 
  for storage before creating dataframe.
  Dict size is 1 million, item is a JSON string.</p>
  
  <pre><code>  ALL=dict()
    ALL[0]=  """{id1: 'Big_JSON' }"""
    for k_id, dd in ALL.items() :
  
     ii+=1 
     if ii &gt; -1 :
      dfi=  pd.io.json.json_normalize(dd)
  
      if ii == 0 :
         ALL_df= dfi    
      else:
         ALL_df= pd.concat((ALL_df, dfi), axis=0)       
         print ii,
  </code></pre>
  
  <p>Is there an fast way to transform into dataframe ?</p>