Creating new layer from the current selection using PyQGIS

Question

Is it possible to create a duplicate layer, only displaying the selection from the layer you are duplicating in QuantumGIS? Similar to ArcGIS -> Create Layer from Selected Features.

I looked at "How to duplicate a layer"

iface = qgis.utils.iface
vl = iface.activeLayer()
iface.addVectorLayer( vl.source(), vl.name(), vl.providerType() )

But can't see how to duplicate only the selected features?

Answer 1

You can retrieve the selected features with

vl = iface.activeLayer()
selectedFeatures = vl.selectedFeatures()

You then need to add a new vector layer. If you want your duplicate layer only in memory (i.e. not persistent), use a memory layer (see the PyQGIS Cookbook) If you want your layer to be persistent, refer to the section about writing vector layers.

Use then the QgsVectorFileWriter.addFeature or QgsVectorLayer.addFeatures method on the retrieved layer / layerwriter to add the features.

In case you have really many features, it might be prudent to use selectedFeaturesIds() and then query and iterate over these to not have to copy all the features into memory.

• Gerardo Jimenez: You can also use "save selection as". First you select the feature(s),then select the layer, right click and choose save selection as. Here you can define the type of file, shape for instance. Works like data export data /selected features in ArcMap

Answer 2

Since QGIS 3.0, there is another approach available. Use the materialize() method from the QgsFeatureSource class.

Here, the code will create a new temporary layer from the selection of all features with the selectedFeatureIds() method from the QgsVectorLayer class. The selection can be adjusted accordingly.

# imports
from qgis.utils import iface
from qgis.core import QgsFeatureRequest, QgsProject
# choose a layer
layer = iface.activeLayer()
# or with: layer = QgsProject.instance().mapLayersByName('LAYER_NAME')[0]
# select all features in the original layer
layer.selectAll()
# create a new layer from selected features
new_layer = layer.materialize(QgsFeatureRequest().setFilterFids(layer.selectedFeatureIds()))
# remove selection in the original layer
layer.removeSelection()
# add a new layer to the map 
QgsProject.instance().addMapLayer(new_layer)

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References:

• Creating Vector layer from selected features with PyQGIS