I'm not sure I understand. Is it something like:
Row 1: Group 1
Row 2: 1
Row 3: 3
Row 4: 100
Row 5: Group 2
Row 6: 44
Row 7: 8
Row 8: Group 3
etc.
And you want to copy items under certain groups.
My main thought is to insert a column to the left and have that column contain the group headings for every row. Thus (with semicolon separating the columns)
Row 1: Group 1; Group 1
Row 2: Group 1; 1
Row 3: Group 1; 3
Row 4: Group 1; 100
Row 5: Group 2; Group 2
Row 6: Group 2; 44
Row 7: Group 2; 8
Row 8: Group 3; Group 3
etc.
Then you can have a formula column C such as =IF(OR(A1={"Group 1","Group 3"}),B1,""). There are more flexible ways than the OR statement, such as having a list of the group names you want in a separate sheet, and using ISERROR(MATCH combination.
So the question is how to get that first column to contain the name of the groups. For that, I'd first have your data starting on row 2. Then put this formula in column A, starting on cell A2: =IF(ISNUMBER(B2),A1,B2). This will check column B, and if it's not a number (i.e., a group name), bring it over to column A. If it is a number (data), then copy the cell above (which is the group name).