I have two shapefiles that I am merging/combining. However, this produces more than 4,000 duplicate records. I need to have only unique records. Is this possible with OGRINFO or OGR2OGR? I've tried Select DISTINCT but it only lets me do select statement on one column/field. I can get a list of unique records but I need to create new shapefil.
asked Aug 14, 2017 at 20:29
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2 Answers
There should be no problem in using many attributes in DISTINCT query at least with the SQLite SQL dialect. Test with ogrinfo:
ogrinfo -dialect sqlite -sql "select distinct geometry, attribute_1, attribute_2 from my_shapefile" my_shapefile.shp
answered Aug 14, 2017 at 20:41
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This works for
ogrinfo, but notogr2ogras the questioner requires. Commented Jun 14, 2018 at 16:11 -
1Works for me with ogr2ogr and gives the same result - as many features written into output file than what gets selected with ogrinfo. Commented Jun 14, 2018 at 16:50
I'm trying to do the same thing, I see in the OGR SQL documentation,
The result of a SELECT with a DISTINCT keyword is a layer with one column (named the same as the field operated on), and one feature per distinct value. Geometries are discarded.
Why they made this choice boggles my mind. But I can confirm that
ogr2ogr -dialect -sqlite -sql "select distinct LINK_ID from layer" out.shp layer.shp
Returns only the out.dbf file, which contains the unique LINK_ID values.
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SQLite dialect does not select geometry field automatically. Have you tried
select distinct geometry, LINK_ID from layer? BTW. it does not help to read the OGR SQL manual if you use the SQLite SQL, read gdal.org/ogr_sql_sqlite.html instead. I have not tried conversion with ogr2ogr myself so you can be right, please tell if it works or not with explicitly selected geometry. Commented Jun 14, 2018 at 16:25 -
@gregmacfarlanane, have you made a test with select geometry,link_id or do you want me to build a test set? Commented Jun 16, 2018 at 11:32