Query in CUSTOM FORMAT REPORT

Hello,

I am trying to create Custom format report for Purchase order , I have field in Purchase order item “pattern”. In pattern i put pattern code with each item.

like p001, p002,p003 ,p001,p002

Now i want to display Item list according Pattern Group wise like. Please can you help me how to make Group on field in report

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Po order -

Pattern 001
item1 89.00 89.00
item2 50.00 40.00

Pattern 002
item 4 45.00 85.00
item5 74.00 90.00

Pattern 003
item7 52.00
item 9 8900