Counting number of selected features in QGIS

Question

I have performed a selection by expression (Attribute table) on a layer that contains thousands of features. I would like to know the number of features in this selection.

Answer 1

Look at the header of the attribute table, it tells you the total number of objects in tables, as well as the filtered and selected ones.

Answer 2

There are several approaches that I may suggest:

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Approach 1: attribute-table

Press Shift + F6 to open the attribute table with selected features only. There will be two values that represent the number of selected features: 'Filtered' and 'Selected'.

You can also see the 'Selected' when simply opening the attribute table with F6. As was answered by @Pierre Vivet.

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Approach 2:

In the left bottom corner, there will be a description of selected features.

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Approach 3: pyqgis python

Similar to @Nenad Stojanovic's answer, however, it is based just on one method called selectedFeatureCount():

from qgis.utils import iface

layer = iface.activeLayer()

print("Selected features count: ", layer.selectedFeatureCount())

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Approach 4: field-calculator

Via opening the Field Calculator and using either num_selected() or num_selected(@layer) expression in the Expression dialogue. It is based on the num_selected() function.

Returns the number of selected features on a given layer. By default works on the layer on which the expression is evaluated.

Also can be achieved with this expression count(1, group_by:=is_selected()), based on the is_selected() function.

Returns True if a feature is selected. Can be used with zero, one or two arguments, see below for details.

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Approach 5: toolbar

Also by means of the "Show statistical summary". Symbolized as a Sigma symbol(), placed in the main QGIS working window.

In the appearing window, you just need to choose the layer in which you are interested choose a random field and tick the 'Selected feature only'. The total number of selected features will be represented in the row called 'Count'.

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References:

• DefKey | QGIS 3.10 keyboard shortcuts

Answer 3

This works fine for me:

from qgis.core import *
import qgis.utils

layer = iface.activeLayer()        
features = layer.selectedFeatures() 
print ("Total count", layer.featureCount())
print ("Selected features count:", len(features))

Answer 4

You can also use QGIS expressions to count the number of selected features in the current layer (e.g. if you use this value for further calculation in the field calculator):

array_length (array_agg ($id, filter:=is_selected(@feature)))

If you want to count the features in another layer, use this expression:

array_length(
    aggregate( 
        'layer_1',  -- change layer name
        'array_agg',
        $id,
        filter:=is_selected('layer_1',@feature) -- change layer name
    )
)