QGIS Expression – Delete Specific Rows from Attribute Table

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I have a shapefile with one column. From that column I want to keep only the records (rows) with value 50 and delete the other rows. So far, I am doing this manually, by selecting the rows with the values I want to delete and I remove them. I was wondering if there is a way to write an expression in QGIS to do this automatically. I have see this post but it's not what I am looking for. Assuming that my attribute table's values is from 20 to 100 with step 10 and the column name is DN, I want to delete all rows except the ones that have a value of 50. Below is a screenshot of the attribute table:

Best Answer

While the layer is selected, open "Select by Expression (Ctrl+F3)" window. Select features using this expression:

DN != 50

Start Editing mode for the layer by clicking yellow pen icon. Click the bin icon to delete the selected features. Finish the Editing mode and save the changes.

Another option would be to use "Extract by Expression" tool. This tool doesn't delete the features, but extract the features which match the expression. In that case, you need to use DN = 50.

Related Solutions

QGIS Contour Lines – Deleting Specific Contour Line Values in QGIS Attribute Table

(Open attribute table) Select them by expression,
start editing,
Delete, which will delete only the selected,
save edits,
stop editing

QGIS Attribute Table – How to Remove Duplicates from Attribute Table by Expression in QGIS

It is not an expression, but there is a tool in QGIS for deleting duplicates called "Delete duplicates by attribute".

Deletes duplicate rows by only considering the specified field / fields. The first matching row will be retained, and duplicates will be discarded.

Optionally, these duplicate records can be saved to a separate output for analysis.

Let's assume there is a polygon layer 'poly_test' with several duplicates, see the image below.

After applying the algorithm with these settings, where the "id" field was used as Fields to match duplicates by

The following output will appear

If there is a need to delete duplicates based on its data "poorness", proceed with the following workflow.

Let's assume there is a polygon layer 'poly_test' with several duplicates, see the image below.

Step 1. Create a field "Quality" using the following expression:

array_count(array("Data1", "Data2", "Data3"), '')

Step 2. Apply the "Extract by expression" with the following expression:

"Quality" = minimum("Quality", group_by:="id")

Step 3. Finally apply the "Delete duplicates by attribute" algorithm (with the "id" field as Fields to match duplicates by) and get the output like this:

Best Answer

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QGIS Contour Lines – Deleting Specific Contour Line Values in QGIS Attribute Table

QGIS Attribute Table – How to Remove Duplicates from Attribute Table by Expression in QGIS

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