v.dissolve is "reclassifying" attributes after dissolve

[qgib]

Author Name: Sarah Popov (@popovs)
Original Redmine Issue: 17203
Affected QGIS version: 2.18.13
Redmine category:grass

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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.

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• Before v-dissolve.JPG (Sarah Popov)
• After v-dissolve [recategorizes consistently].JPG (Sarah Popov)

[qgib]

Author Name: Giovanni Manghi (@gioman)

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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?

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• status_id was changed from Open to Feedback

[qgib]

Author Name: Sarah Popov (@popovs)

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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?

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• resolution was changed from to invalid
• status_id was changed from Feedback to Closed