pyqgispythonqgis
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?
This is a somewhat older question and the correct answer has changed with recent versions of QGIS.
PostGIS Manager has been deprecated, and superseded by DB Manager which works for both PostGIS and SpatiaLite.
DB Manager is installed by default and accessible under the Database > DB Manager menu entry. That will open up the DB Manager window.
Select the database you want to add a layer too and then click Table > Create table. If you don't have a database selected when you click on the Table menu entry, the create table option will not be there.
That will open up the create table dialog which is very similar to the one accessed by Layer > New > New SpatiaLite Layer but with a different layout.
The options are mostly the same with the largest difference being that the New Spatialite Layer dialog allows access to the Specify CRS dialog which makes selecting your coordinate system easier. The Create table dialog requires that you know the SRID number beforehand to enter it.
I modified your code to consider a polygon vector layer. However, if you get the features of the original layer, you only need a little portion of your original code for working adequately (without any editing session if you use the QgsDataProvider class).
This is my code:
input = "/home/zeito/pyqgis_data/polygon8.shp"
layer = QgsVectorLayer(input,"polygon","ogr")
feats = [ feat for feat in layer.getFeatures() ]
temp = QgsVectorLayer("Polygon?crs=epsg:32612", "result", "memory")
QgsProject.instance().addMapLayer(temp)
temp_data = temp.dataProvider()
attr = layer.dataProvider().fields().toList()
temp_data.addAttributes(attr)
temp.updateFields()
temp_data.addFeatures(feats)
When above code was running at the Python Console (Ctrl+Alt+P) of QGIS, fields of original layer were correctly copied at the memory layer named "result"; as can be observed at the next image. It worked for me.
On the other hand, your approach of set attributes to a list of fields instead a list of values is correct because if I comment these code lines:
attr = layer.dataProvider().fields().toList()
temp_data.addAttributes(attr)
it doesn't populate the fields with data; as it also observed at the next image:
Best Answer
You can retrieve the selected features with
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 the memory.