Hi Athanasius,

First of all thank you very much for your try. I tried with your code, but still that is also giving some incorrect results. Below fyi.

Input data that i have considered below

7900724666,200906888,20180416,20180522
7900724666,200906888,20180601,20180720
7900724666,200906888,20180406,20180411
7900724677,200906872,20180301,20180330
7900724677,200906871,20180101,20180228
7900724677,200906873,20180401,20180420
7900724688,200906881,20180101,20180228
7900724688,200906881,20180303,20180330
7900724688,200906882,20180404,20180430
7900724688,200906883,20180508,20180620
7900724699,200906891,20180101,20180228
7900724699,200906891,20180303,20180330
7900724699,200906892,20180404,20180430
7900724699,200906893,20180508,
7900724611,200906888,20180416,20180522
7900724611,200906889,20180724,20180728
7900724611,200906889,20180601,20180720
7900724611,200906888,20180730,20180830
7900724611,200906890,20180905,20180930
7900724611,200906890,20181005,20181030
7900724611,200906890,20181104,
7900724622,200906868,20180416,20180522
7900724622,200906869,20180601,20180720
7900724622,200906869,20180724,20180728
7900724622,200906868,20180730,20180830
7900724622,200906890,20180905,20180930
7900724622,200906890,20181005,20181030
7900724622,200906890,20181104,
[download]

The output which i have got is below

7900724666,200906888,20180416,20180411
7900724688,200906881,20180101,20180330
7900724699,200906891,20180101,20180330
7900724611,200906889,20180724,20180720
7900724611,200906890,20180905,
7900724622,200906869,20180601,20180728
7900724622,200906890,20180905,
[download]

Here 1st line and 4th line in output are incorrect: Ex:

7900724611,200906889,20180724,20180720
[download]

Here expected result in output 4th line is 7900724611,200906889,20180601,20180728