docs: def f1_score(y, y_pred):
      """F1 score
  
      f1_score = 2 * precision*recall / (precision + recall)
      
      Parameters:
      -----------
      y : vector, shape (n_samples,)
      The target labels.
  
      y_pred : vector, shape (n_samples,)
      The predicted labels.
      
      Returns:
      --------
      f1_score : float
      
      """
  
      p = precision(y, y_pred)
      r = recall(y, y_pred)
  
      return 2*p*r / (p+r)