//Build neural network
  model = tf.sequential();
  model.add(tf.layers.dense({inputShape: [documents.length], units: 100}));
  model.add(tf.layers.dense({units: 4}));
  model.compile({loss: 'categoricalCrossentropy', optimizer: 'sgd'});

  model.fit(xs, ys, {epochs: 1000});

tf.layers.dense({inputShape: [xs.shape[0]], units: 100})

model.add(tf.layers.dense({inputShape: b, units: 100}));

model.add(tf.layers.dense({inputShape: [27, 48], units: 100}));