Extract by expression in the graphical modeller in QGIS [closed]

Question

Using the graphical modeller (QGIS 3.22.14), I'm implementing the procedure described here: Determining the direction of polygons? to determine the orientation of polygons in a vector layer. I'm struggling with the part with a selection by expression (step 6 in SE)

$length < (minimum(  $length ,  "unique_id" )+ 0.1)

I've implemented this as in the images attached, but I'm getting errors: only one group is generated and the rest is never matched. Note that I've produced the unique_id_z and it is already in the layer.

How would you go about implementing this step?

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About my QGIS instance:

QGIS version
3.22.14-Białowieża
QGIS code revision
4cde646cf9
Qt version
5.15.3
Python version
3.10.6
GDAL/OGR version
3.4.1
PROJ version
8.2.1
EPSG Registry database version
v10.041 (2021-12-03)
GEOS version
3.10.2-CAPI-1.16.0
SQLite version
3.37.2
PDAL version
2.3.0
PostgreSQL client version
14.5 (Ubuntu 14.5-0ubuntu0.22.04.1)
SpatiaLite version
5.0.1
QWT version
6.1.4
QScintilla2 version
2.11.6
OS version
Linux Mint 21




Active Python plugins
dissolve_related
1.2
dissect_dissolve_overlaps
0.3
processing_umep
1.7.8
google-street-view-layer-master
0.1
OpenICGC
1.1.11
latlontools
3.6.7
dissolve_adjacent_polygons
0.1
QuickOSM
2.1.1
Spanish_Inspire_Catastral_Downloader
1.1
area_weighted_average
0.2
QPackage
1.5
pointsamplingtool
0.5.4
kmltools
3.1.27
processing_saga_nextgen
0.0.7
LAStools
1.4
db_manager
0.1.20
MetaSearch
0.3.5
processing
2.12.99
sagaprovider
2.12.99
``

Answer 1

The problem was somewhere else. I found that I was using @row_label instead of @row_number for generating unique ids (unique_id_z), thus producing a column filled with NULLS. I've changed it and now it works.