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I'm conducting aggregate function in QGIS. But since the feature number is high, the process is very slow. Is there a way to speed up the calculation process. I'm not good in other softwares.

By using this function: sum("lengths", "ID-1" ) I aimed to get the sum of the lengths field from all features in the layer with the same ID-1 value as the current feature.

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    how is your data stored? is there an index on ID1?
    – Ian Turton
    Jun 22 at 10:07
  • I created by using $id from field calculator. They are integer. There is not an index I suppose.
    – Eren E
    Jun 22 at 10:10
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    then export your data into a databse and add an index to it
    – Ian Turton
    Jun 22 at 10:40
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    I'm very new in this field. So I'm not sure how to do it. Could you suggest a tutorial or any other thing to follow?
    – Eren E
    Jun 22 at 10:42

1 Answer 1

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What if you try a Virtual Field with PyQGIS from the QGIS Python Console (Ctrl+Alt+T).

from qgis.utils import iface
from qgis.core import QgsVectorLayer, QgsField
try:
    from PyQt5.QtCore import QVariant
except ImportError:
    from qgis.PyQt.QtCore import QVariant

layer = iface.activeLayer()

layer.startEditing()
field = QgsField('calc', QVariant.String)
layer.addExpressionField('sum("lengths","ID_1")', field)
layer.commitChanges()
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  • I got null results from this function.
    – Eren E
    Jun 22 at 16:43
  • Which data types are your input fields ?
    – Taras
    Jun 22 at 16:43
  • lengths field is Decimal, ID field is whole number Int 64
    – Eren E
    Jun 22 at 16:51
  • Can you please share a piece of your data ?
    – Taras
    Jun 22 at 17:03

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