Cut polygon shapefiles by line shapefiles grouped by unique id

Question

I have a polygon shapefile that consists of different polygon features. Each polygon features can be identified by a unique group_id. I also have a line shapefile with different straight line features that lie on top of the polygons. Similar to the polygon file, each line feature has a unique 'group_id', which are the same as the ones found in the polygon file.

I would like to cut each polygon feature by these line features, but only those that share the same group_id. I'm aware I can use the Split by Line features, however this will use all line features to cut all polygon features, neglecting the group_id.

Any ideas how I could perform some sort of group by function?

Answer 1

Here's a three step approach.

1. Use Split Vector Layer to split both the polygons and lines by the unique id (eg fid). This should give you two directories of files, one for the polygons and the other for the lines - with the same names.

2. Use Split by Lines in Batch Processing Mode.

   • Use Add files by pattern... to load up the polygon files in the Input layer field.
   • Then use Calculate by Expression to load the line files in the Split layer field eg <lines directory> + base_file_name( @INPUT)`.
   • You can similarly use Calculate by Expression to create the names for the Output files

3. Finally, use Merge Vector Layers to merge the files from step (2) into a single file.