Omnis Technical Note TNNO0007

Removing duplicate rows from a list

For Omnis Classic
By Omnis Technical Support (with Developer collaboration)

Is there a fast and effective technique for removing duplicate rows from a list?
Of course there is - here's how.

This routine can come in two basic forms:
1. A straight removal of rows where the value in the same column of existing rows is duplicated.
2. The removal of duplicate rows is created when two lists are merged

The following routine was the fastest of all the methods submitted.
myList: 1578 rows of which 250 are scattered duplicates of myCol.

Set current list (myList)
Set sort field (myCol)
Sort list
Set search as calculation {myList(1,#L)=myList(1,#L-1)}
Search list (Select matches (OR),Deselect non-matches (AND))
Delete selected lines

Submitted by Daniel Bogesdorfer: time = 2 secs