Data filtering large array

I need to filter data in a large dataset (300.000+). The column which needs filtering consists of values 'a|b' per row. There are a lot of the same 'a|b' values in the column, but not every combination has the same length (i.e. 'a|b' is 4x in the column, but 'c|b' is 9x in the column).

The first combination needs to stay, in this case 'a|b' and all other options with 'b' as second number needs to be deleted.

Example: Column: a|b, a|b, a|b, c|b, c|b, d|e, d|e, f|e, f|e, f|e.

The solution should be: a|b, a|b, a|b, d|e, d|e.

Any help would be greatly appreciated.

[Geoff Hayes]

Paul - you may want to attach a file that includes a subset of your data so that we can get a better idea of what its contents. When you stay that the not every combination has the same length, do you mean that some rows have four columns, and others have nine?