Deleting selected features using PyQGIS

Question

I have a shapefile with only one field "DN". I would like to delete all features which does not have specific value of the field. Let's say the "DN" can be 1,2 or 3.

So far I was able to find out how to select Features and how to delete feature, but I did not succeed to combine them. Let's say I want only features with "DN" = 3 to remain:

Selection of the Features found here : Filter features based on their attributes using Python, however, I do not know if it does what it is supposed to do since I did not find the way how to check what is inside.

select = layer.getFeatures(QgsFeatureRequest().setFilterExpression(u'"DN"!=3'))

delete features found in the PyQGIS Developer Cookbook

res = Ilayer.dataProvider().deleteFeatures()

As far as I know, the deleteFeatures() requires "ID"s of the features, but I have no idea how to get them from from select which is QgsFeatureIterator.

score 27 · Accepted Answer · edited Apr 11 '22 at 10:59

27

You can loop over the iterator and get the id() for every feature in it:

with edit(layer):
    # build a request to filter the features based on an attribute
    request = QgsFeatureRequest().setFilterExpression('"DN" != 3')
# we don't need attributes or geometry, skip them to minimize overhead.
# these lines are not strictly required but improve performance
request.setSubsetOfAttributes([])
request.setFlags(QgsFeatureRequest.NoGeometry)

# loop over the features and delete
for f in layer.getFeatures(request):
    layer.deleteFeature(f.id())

or with QGIS < 2.12

request = QgsFeatureRequest().setFilterExpression('"DN" != 3')
request.setSubsetOfAttributes([])
request.setFlags(QgsFeatureRequest.NoGeometry)
ids = [f.id() for f in layer.getFeatures(request)]
layer.startEditing()
for fid in ids:
    layer.deleteFeature(fid)
layer.commitChanges()

edited Apr 11 '22 at 10:59

Taras

32,823
4
66
137

answered Aug 29 '14 at 14:32

Matthias Kuhn

27,780
3
88
129

Thank you, that was that! I just noticed that the FilterExpression was wrong (not u'"DN"=2||"DN"=1' but u'"DN"!=3' should be used). Please if you would edit your answer for this not to confuse other viewers. – MasterPJ Aug 29 '14 at 14:44
isn't it layer.dataProvider().deleteFeatures(ids)? – mbernasocchi Aug 13 '15 at 12:34
Using dataProvider() is possible but I prefer to work directly on the layer since this way the changes are communicated internally (to the map canvas, attribute table...) and other reasons. – Matthias Kuhn Aug 13 '15 at 21:34
2

layer.dataProvider().deleteFeatures(ids) has thrown crashes for me when layer.deleteFeature(fid) didnt... Bad crashes. The kind that cause a seg fault and kill qgis. The kind that take 6 hours to find... stick with the answer posted here. Bums me out because layer.dataProvider().deleteFeatures(ids) is all through my code and now I've got to fix it all. – Mr Purple Mar 09 '16 at 02:29

Taras · Answer 2 · 2022-11-28T07:40:36.747

There is also a possibility of using the deleteSelectedFeatures() method from the QgsVectorLayer class for deleting selected features:

# choose an active layer
layer = iface.activeLayer()
make own selection
field_name = "DN" # specify your field
field_values = (1,2,3) # specify values for features that you want to retain
expression = f'"{field_name}" in {field_values}'
layer.selectByExpression(expression)
delete selected features
if layer.selectedFeatureCount() > 0:
    layer.startEditing()
    layer.deleteSelectedFeatures()
    layer.commitChanges()

Deleting selected features using PyQGIS

2 Answers2

or with QGIS < 2.12

make own selection

delete selected features

Linked