text: # -*- coding: utf-8 -*-
  """Test for panel robust covariance estimators after pooled ols
  this follows the example from xtscc paper/help
  
  Created on Tue May 22 20:27:57 2012
  
  Author: Josef Perktold
  """
  
  from statsmodels.compat.python import range, lmap
  import numpy as np
  from numpy.testing import assert_almost_equal
  
  from statsmodels.regression.linear_model import OLS
  from statsmodels.tools.tools import add_constant
  import statsmodels.stats.sandwich_covariance as sw
  
  
  def test_panel_robust_cov():
      import statsmodels.datasets.grunfeld as gr
      from .results.results_panelrobust import results as res_stata
  
      dtapa = gr.data.load_pandas()
      #Stata example/data seems to miss last firm
      dtapa_endog = dtapa.endog[:200]
      dtapa_exog = dtapa.exog[:200]
      res = OLS(dtapa_endog, add_constant(dtapa_exog[['value', 'capital']],
                prepend=False)).fit()
  
      #time indicator in range(max Ti)
      time = np.asarray(dtapa_exog[['year']])
      time -= time.min()
      time = np.squeeze(time).astype(int)
  
      #sw.cov_nw_panel requires bounds instead of index
      tidx = [(i*20, 20*(i+1)) for i in range(10)]
  
      #firm index in range(n_firms)
      firm_names, firm_id = np.unique(np.asarray(dtapa_exog[['firm']], 'S20'),
                                      return_inverse=True)
  
      #panel newey west standard errors
      cov = sw.cov_nw_panel(res, 0, tidx, use_correction='hac')
      #dropping numpy 1.4 soon
      #np.testing.assert_allclose(cov, res_stata.cov_pnw0_stata, rtol=1e-6)
      assert_almost_equal(cov, res_stata.cov_pnw0_stata, decimal=4)
  
      cov = sw.cov_nw_panel(res, 1, tidx, use_correction='hac')
      #np.testing.assert_allclose(cov, res_stata.cov_pnw1_stata, rtol=1e-6)
      assert_almost_equal(cov, res_stata.cov_pnw1_stata, decimal=4)
  
      cov = sw.cov_nw_panel(res, 4, tidx)  #check default
      #np.testing.assert_allclose(cov, res_stata.cov_pnw4_stata, rtol=1e-6)
      assert_almost_equal(cov, res_stata.cov_pnw4_stata, decimal=4)
  
      #cluster robust standard errors
      cov_clu = sw.cov_cluster(res, firm_id)
      assert_almost_equal(cov_clu, res_stata.cov_clu_stata, decimal=4)
  
      #cluster robust standard errors, non-int groups
      cov_clu = sw.cov_cluster(res, lmap(str, firm_id))
      assert_almost_equal(cov_clu, res_stata.cov_clu_stata, decimal=4)
  
      #Driscoll and Kraay panel robust standard errors
      rcov = sw.cov_nw_groupsum(res, 0, time, use_correction=0)
      assert_almost_equal(rcov, res_stata.cov_dk0_stata, decimal=4)
  
      rcov = sw.cov_nw_groupsum(res, 1, time, use_correction=0)
      assert_almost_equal(rcov, res_stata.cov_dk1_stata, decimal=4)
  
      rcov = sw.cov_nw_groupsum(res, 4, time) #check default
      assert_almost_equal(rcov, res_stata.cov_dk4_stata, decimal=4)
  