Hi Jagadish, I need to replace the missing values for distance with mean of distance and group by carrier, origin and dest. Please find the sample data below: date sched_dep_time dep_time sched_arr_time arr_time carrier flight tailnum origin dest distance 1/1/2013 515 517 819 830 UA 1545 N14228 EWR IAH 1400 1/1/2013 529 533 830 850 UA 1714 N24211 LGA IAH 1416 1/1/2013 540 542 850 923 AA 1141 N619AA JFK MIA . 1/1/2013 545 544 1022 1004 B6 725 N804JB JFK BQN 1576 1/1/2013 600 554 837 812 DL 461 N668DN LGA ATL 762 1/1/2013 558 554 728 740 UA 1696 N39463 EWR ORD 719 1/1/2013 600 555 854 913 B6 507 N516JB EWR FLL 1065
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