title: What is the structure of ATIS (Airline Travel Information System) dataset
body: <p>When I use ATIS (Airline Travel Information System) dataset(<a href="http://lisaweb.iro.umontreal.ca/transfert/lisa/users/mesnilgr/atis/" rel="nofollow">http://lisaweb.iro.umontreal.ca/transfert/lisa/users/mesnilgr/atis/</a>) to do research in recurrent-neural-network. I am confused with it's structure.</p>
  
  <p>For example, after using <code>data = pickle.load(open("./dataset/atis.fold0.pkl",  "rb"),encoding='iso-8859-1')</code> to load the atis.fold0.pkl, I use <code>print (np.shape(data_train))</code> to get <code>(4,)</code>. I think the data[0] is the training set, the data[1] is the valid set, the data[2] is the test set and the data[3] is the dict. </p>
  
  <p>But when I use <code>print(np.shape(data[0]))</code>, I get <code>(3, 3983)</code>. I wonder why I get 3 rows in it? what's the difference between these three rows. </p>
  
  <p>And what's the difference between file atis.fold0.pkl, atis.fold1.pkl, atis.fold2.pkl, atis.fold3.pkl, atis.fold4.pkl?</p>