QGIS Select double feature by attributes

Question

There is this point shapefile in QGIS (2.12). There is one column with the street name and one with the housenumber.

Is it possible to select all features that have the same street name and housenumber (not one by one, but automatically all that are alike)? If yes, what tool do I have to use or what is the expression if I "select by expression"?

Answer 1

you can use a custom function in the 'Select by Expression' Editor. This loads your active layer from the QgsInterface and makes a list combined out of your 2 columns. Then it checks for every value pair, wheter it is more then one time in the list. I yes it Returns 'true' and selects the Feature. If the value pair is only once in the list, then the Feature ist not selected.

The function Looks like this:

from qgis.core import *
from qgis.gui import *
from qgis.utils import iface

@qgsfunction(args=-1, group='Custom')
def findDuplicates(value1, feature, parent):
layer = iface.activeLayer()
combinedList =[]
for streetnumber in layer.getFeatures():        
    combinedList.append(str(streetnumber.attribute('COLUMN_NAME_OF_STREETS')) + str(streetnumber.attribute('COLUMN_NAME_OF_HOUSE_NUMBERS')))
if combinedList.count(value1[0]+str(value1[1]))>1:
    return True
else:
    return False

You save this function and call it like this:

Then all Features which are dublicates by housenumber and street are selected.

I hope this is the solution for your Problem. Unfortunately I have no idea for an Expression.

Answer 2

Group Stats Plugin lets you do grouping based on columns and find aggregates such as COUNT, SUM, AVG etc. There is also option to show selected features on the map but I could not figure out whether we can filter the result e.g. count > 1

Edit: Including Select by Expression again

Option 1: Direct menu

Click on Select by Expression menu

Option 2: Through attributes table

Right click on point layer => Open attributes table => Select Advanced Filter (Expression)

Set the filter, you can do it on multiple columns with AND OR conditions

Select the records by clicking on left top corner => select Show Selected Features

You can the selected features on the map (yellow color)