Delete rows from table based on conditions

[CLemons]

I want to delete certain rows from a table.
The conditions are : if column 1 = colum 2 ( like 1 in the example below)
and if the combination of colum 1 and column 2 has shown up in the table before ( like 2 and 4 in the example below)

1 Metabolite A Metabolite A
2 Metabolite A Metabolite B
3 Metabolite A Metabolite C
4 Metabolite B Metabolite A
5 Metabolite B Metabolite C

[dflak]

Assuming that these are in columns A, B and C.
In column D make a "composite" of the two Columns: =IF(B2<C2,B2&":"&C2,C2&":"&B2) this formula concatenates them in alphabetical order. So A & B and B & A both come out as A:B.

In column E we determine whether to keep the row. =AND(MATCH(D2,$D$1:$D$6,0)=ROW(),B2<>C2)

The MATCH(D2,$D$1:$D$6,0)=ROW() evaluates to true for the first occurrence of the composite. the B2<>C2 part checks to see if the cells are not alike.