Count points in polygon grouping by attribute using PyQGIS

Question

I have a point layer with an attribute table like this:

id_point  class
       1      A
       2      B
       3      A
       4      C
       5      B
...

What I need is to count how many points of any class are in every polygon. Something like this

id_pol   A   B   C
  pol1   1   2   0
  pol2   1   0   1
...

Is there a way to count points within polygons grouping by a point attribute using Python in QGIS 3?

I think QGIS 2 had a Count Unique Features by Polygon but I can't find it in QGIS 3.

Answer 1

Use this script:

from PyQt5.QtCore import QVariant

# layers
polygon_lyr = QgsProject.instance().mapLayersByName("Polygons")[0]
point_lyr = QgsProject.instance().mapLayersByName("Points")[0]

# index number of "class" field 
field_index = point_lyr.fields().indexFromName('class')

# unique class names
unique_classes = point_lyr.uniqueValues(field_index)

polygon_lyr.startEditing()

# add a field for each class to polygon layer
for field_name in unique_classes:
    if polygon_lyr.fields().indexFromName(field_name)==-1:
        polygon_lyr.addAttribute(QgsField(field_name, QVariant.Int))

for feat in polygon_lyr.getFeatures():
    g = feat.geometry()
    req = QgsFeatureRequest(g.boundingBox()) # for performance
    classes = [p["class"] for p in point_lyr.getFeatures(req) if g.contains(p.geometry())]
    class_numbers_in_polygon = {cls: classes.count(cls) for cls in unique_classes}

    # add unique class numbers in polygon to the related field
    for cls in class_numbers_in_polygon:
        feat[cls] = class_numbers_in_polygon[cls]
        polygon_lyr.updateFeature(feat)

polygon_lyr.commitChanges()