Flatten Subarray Keys into Category Columns with a Sortable Aggregated Inverse Index

How it works

1. 1.Run the Manual Trigger; a Code node emits a fictional hierarchical object with a variable number of keys
2. 2.The flatten node decomposes each subarray into rows carrying category, positionIndex, id, name and qty
3. 3.The inverse-index node aggregates row counts and id lists per category and sorts descending with a rank field
4. 4.If routes categories with rowCount greater than 2 to one branch and the rest to the other via NoOp endpoints
5. 5.Merge appends both branches and Set fixes category, rowCount, ids and rank as the final output

Use cases

• Flattening hierarchical inventory-style data with variable groups before reporting
• Building an inverse index linking each category to its row ids
• Ranking categories by row volume for prioritization

Requirements

• n8n 2.44.6 with code, if, merge, set, noOp, stickyNote and manualTrigger nodes
• No credentials and no network calls — fully local processing
• For real input: replace the sample-emitting node with a source emitting item.json.groups of the same schema; adjust the threshold in the If condition

Setup and testing in n8n

1. Import the JSON into n8n and execute the demo manually from the Manual Trigger
2. Verify flattened rows carry the correct category and zero-based positionIndex
3. Verify the final output has four items ordered 4,3,2,1 with correct ids
4. Edge test: add an empty subarray or a non-array key and confirm safe skipping

Service Value

Ready-made workflow template for automation delivery and service execution.