Bug report #15822
Singleparts to multi-part polygon algorithm uses NULL values also
|Affected QGIS version:||2.14.2||Regression?:||No|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:||fixed/implemented|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||23742|
I have a polygon shapefile with an attribute villageID, in which some polygons have the same attribute value and so they should together form a single multi-part polygon. Some other polygons have NULL in this villageID field. When I run the tool Vector>Geometry Tools>Singleparts to Multipart (from the menu or from Procsesing Toolbox, and whether I use the GDAL version or the QGIS geoalgorithm version), the resulting shapefile does merge the repeated villageIDs into multi-part polygons. But it ALSO merges ALL the polygons that had this field = NULL into a SINGLE multi-part polygon. In effect, it is treating all NULL values as equal, when in fact it should treat NULL as 'not known' and ignore those polygons. If I run a 'find duplicates' query in MS-ACCESS on the attribute table dbf, the query ignores those rows where villageID=NULL, which IMHO is the correct method.
Revert "[processing] handle NULL values in the Singleparts to multiparts (fix #15822)"
This reverts commit a944f7c4c1010767abb811200686e327040c2d32.