QGIS python script to update a field with a autoincrement value using an xy order of features.

qgis_script_to_enumerate_elements_by_xy.py

##
# QGIS python script to update a field with a autoincrement value using an xy order of features.
# Created at: March 2018

import operator

# Attribute field to update
FIELD_TO_AUTOINCREMENT = 'id'
START_AT = 1  #0

layer = iface.activeLayer()

autoincrement_idx = layer.fieldNameIndex(FIELD_TO_AUTOINCREMENT)

a_feat = []
fid_new_values = {}

for f in layer.getFeatures():
    bbox = f.geometry().boundingBox() 
    item = {'x': bbox.xMinimum(),'y': bbox.yMaximum(), 'id': f.id(), 'old_field': f['id']}    
    #print(item)
    a_feat.append(item)


## Sorting
a_feat.sort(key=operator.itemgetter('x'))
#items that compare equal retain their original order.
a_feat.sort(key=operator.itemgetter('y'), reverse=True)

num = START_AT
for i in a_feat:
    #print(i)
    fid_new_values[i["id"]] = num
    num = num + 1
    
layer.startEditing() 
for feat in layer.getFeatures():
    feat[autoincrement_idx] = fid_new_values[feat.id()]
    layer.updateFeature(feat)

layer.commitChanges()