title: What is "random-state" in sklearn.model_selection.train_test_split example?
body: <p>Can someone explain me what <code>random_state</code> means in below example?</p>
  <pre><code>import numpy as np
  from sklearn.model_selection import train_test_split
  X, y = np.arange(10).reshape((5, 2)), range(5)
  
  
  X_train, X_test, y_train, y_test = train_test_split(
      X, y, test_size=0.33, random_state=42) 
  </code></pre>
  <p>Why is it hard coded to 42?</p>