code: def get_cv_idxs(n, cv_idx=0, val_pct=0.2, seed=42):
      
      np.random.seed(seed)
      n_val = int(val_pct*n)
      idx_start = cv_idx*n_val
      idxs = np.random.permutation(n)
      return idxs[idx_start:idx_start+n_val]
docs: Get a list of index values for Validation set from a dataset
      
      Arguments:
          n : int, Total number of elements in the data set.
          cv_idx : int, starting index [idx_start = cv_idx*int(val_pct*n)] 
          val_pct : (int, float), validation set percentage 
          seed : seed value for RandomState
          
      Returns:
          list of indexes