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I have a poly line layer where each feature has a Geometric Length and numerical ID. Some of these IDs are duplicates. I would like to be able to select the longest line from each set of duplicates to create a new layer with just the unique IDs.

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QGIS 2.18 case:

  1. Open attribute table
  2. Activate Select by expression
  3. Type $length = maximum($length, group_by:= "id")
  4. Click on [Select]
  5. Save As... (Save only selected features)
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  • Thank you. I didn't know about 'group_by'.
    – Steve H
    Oct 2 '17 at 2:33
  • Thanks @SteveH , Yes Aggregates group is relatively new Changelog for QGIS 2.16. I think they are extremely useful.
    – Kazuhito
    Oct 2 '17 at 2:44

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