fix data test error

Author: jiwidi

02-Forecasting_models.ipynb

@@ -163,7 +163,7 @@
    "source": [
     "#Also add the naive mean average value\n",
     "mean = df_training.pollution_today.mean()\n",
-    "mean = np.array([mean for u in range(len(df_training))])\n",
+    "mean = np.array([mean for u in range(len(df_test))])\n",
     "resultsDict['Naive mean'] = evaluate(df_test.pollution_today, mean)\n",
     "predictionsDict['Naive mean'] = mean\n",
     "resultsDict['Yesterdays value'] = evaluate(df_test.pollution_today, df_test.pollution_yesterday)\n",