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Within a vector layer I have dissolved 25k polygons into 43 different categories of land ownership (Ld_Use_Des). But now I want to further ''group'' them. For example I want to select Mineral Rights and Recreational and add them to Governmentally_owned (existing category in the attribute table).

screenshot of attribute table

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    Update the column in question using a conditional expression.
    – Erik
    Mar 28 at 10:06
  • do you mean in field calculator?
    – N_LLC
    Mar 28 at 11:11
  • Yes, the field calculator is very well capable of doing, what you seem to ask for. You just need to define for yourself, which categories you want to summarize.
    – Erik
    Mar 28 at 11:57

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One way to do this is to run the processing function Statistics by Categories with settings as shown here: enter image description here

Then export this to a csv field with field ld_use_des the only field that is exported. Then edit this in notepad or excel - add a new category field:

enter image description here

Then add the edited csv file back as a text delimited layer and join it to the original ownership layer using the common field. You can then export that as a new dataset and the categories will be permanently set, or use field calculator to set a new field in the existing layer.

Alternative method with field calculator - quicker method. enter image description here

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  • I think there should be a more efficient way in which you stay inside qgis
    – N_LLC
    Mar 28 at 11:11
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    If you have a small number of categories then a conditional expression would be easier but if there are many codes with many categories this way may be quicker.
    – Aquamarine
    Mar 28 at 11:37
  • Original post edited with field calculator method
    – Aquamarine
    Mar 28 at 13:39

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