Bug report #17203

v.dissolve is "reclassifying" attributes after dissolve

Added by Sarah Popov about 3 years ago. Updated almost 3 years ago.

Status:Closed
Priority:Normal
Assignee:-
Category:GRASS
Affected QGIS version:2.18.13 Regression?:No
Operating System: Easy fix?:No
Pull Request or Patch supplied:No Resolution:invalid
Crashes QGIS or corrupts data:No Copied to github as #:25102

Description

I have a polygon with 5 features, classified 1-5, with 1 being light yellow gradating to 5 being dark blue. Some are split in half (see right half of first screenshot) so I dissolve by attribute using v.dissolve. The resulting output consistently "reclassifies" my 5 features like so:

1 (light yellow) becomes -> 5 (dark blue)
2 (green) -> 1 (light yellow)
3 (blue-green) -> stays as 3!
4 (mid blue) -> stays as 4
5 (dark blue) -> 2 (green)

You can see the attribute & corresponding color changes in the second screenshot. The dissolve worked great (the seams between polygons are gone), only the attributes were all shuffled around! I checked my polygons for any errors and there don't appear to be any so I believe it may be the dissolve function.

Before v.dissolve
https://imgur.com/a/EU2U1

After v.dissolve (feature attributes are reclassified)
https://imgur.com/a/uu6uC

PS - this is my first bug report issued, so please let me know if there is anything to be fixed or done better in this report.

Before v-dissolve.JPG - Before v.dissolve (128 KB) Sarah Popov, 2017-09-26 07:25 PM

After v-dissolve [recategorizes consistently].JPG - After v.dissolve (133 KB) Sarah Popov, 2017-09-26 07:26 PM

History

#1 Updated by Giovanni Manghi almost 3 years ago

  • Status changed from Open to Feedback

Can you attached the data?
You did the operation within the GRASS plugin or in the Processing toolbox?
Have you tried different dissolve tools in the Processing toolbox?

#2 Updated by Sarah Popov almost 3 years ago

Giovanni Manghi wrote:

Can you attached the data?
You did the operation within the GRASS plugin or in the Processing toolbox?
Have you tried different dissolve tools in the Processing toolbox?

I've tried to replicate this but I can't - I guess I just was having a bad GIS day that day. Can you close this ticket?

#3 Updated by Giovanni Manghi almost 3 years ago

  • Resolution set to invalid
  • Status changed from Feedback to Closed

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