# Split rows into equal buckets

Shape / rows

A variant of [Number or rank rows](https://meridian.online/operations/number-or-rank-rows).

Assign each row to one of N buckets of equal size, in order.

Page: <https://meridian.online/operations/number-or-rank-rows/split-rows-into-equal-buckets>

## Status

Runs as a SQL step.

arcform carries it as a `sql:` step today.

## The DuckDB step

split rows into N buckets of equal size, in order

It reads the `orders` table the proofs share. Create it first:

```sql
CREATE TABLE orders AS SELECT * FROM (VALUES
  (1,  'Alice Ng',      'north', DATE '2026-01-03', 120.00, 'widget', 'a|b',   '{"channel":"web","items":[1,2]}'),
  (2,  'alice ng',      'north', DATE '2026-01-05',  80.50, 'gadget', 'b',     '{"channel":"shop","items":[3]}'),
  (3,  'Bob  Okafor',   'south', DATE '2026-01-05', 300.00, 'widget', 'a|c',   '{"channel":"web","items":[4,5,6]}'),
  (4,  'Carla Díaz',    'east',  DATE '2026-01-09',  NULL,  'gizmo',  NULL,    '{"channel":"web","items":[]}'),
  (5,  'Bob Okafor',    'south', DATE '2026-01-12',  45.25, 'gadget', 'c',     '{"channel":"phone","items":[7]}'),
  (6,  'Dev Patel',     'west',  DATE '2026-01-12', 510.00, 'widget', 'a',     '{"channel":"web","items":[8,9]}'),
  (7,  'Carla Diaz',    'east',  DATE '2026-01-20',  99.99, 'gizmo',  'b|c',   '{"channel":"shop","items":[10]}'),
  (8,  'Dev Patel',     'west',  DATE '2026-02-02', 510.00, 'widget', 'a',     '{"channel":"web","items":[8,9]}'),
  (9,  'Eve Larsen',    NULL,    DATE '2026-02-03',  15.00, 'gadget', NULL,    '{"channel":"web","items":[11]}'),
  (10, 'Alice Ng',      'north', DATE '2026-02-10', 220.00, 'gizmo',  'a|b|c', '{"channel":"phone","items":[12,13]}')
) t(order_id, customer, region, order_date, amount, product, tags, meta);
```

Then run the statement:

```sql
CREATE TEMP TABLE bucketed AS
SELECT order_id, amount,
       ntile(5) OVER (ORDER BY amount NULLS LAST, order_id) AS fifth,
       ntile(4) OVER (ORDER BY amount NULLS LAST, order_id) AS quarter
FROM orders;
SELECT * FROM bucketed ORDER BY amount NULLS LAST, order_id;
SELECT CASE WHEN ((SELECT list(ids ORDER BY fifth) FROM (SELECT fifth, list(order_id ORDER BY amount NULLS LAST, order_id) AS ids FROM bucketed GROUP BY fifth)) = [[9, 5], [2, 7], [1, 10], [3, 6], [8, 4]] AND (SELECT list(n ORDER BY quarter) FROM (SELECT quarter, count(*) AS n FROM bucketed GROUP BY quarter)) = [3, 3, 2, 2]) THEN 'as expected' ELSE error('ten rows in five buckets were not five pairs in amount order, or in four buckets were not sized 3, 3, 2 and 2') END AS verdict;
```

It needs nothing installed beyond DuckDB itself.

## What other tools call it

Meridian's classification; an independent blind rating agreed on 95.7% of 324 rows (variant, version 3).

- Apache DataFusion: [`ntile`](https://datafusion.apache.org/user-guide/sql/window_functions.html) (read 2026-09-27)
- DuckDB: [`ntile`](https://duckdb.org/docs/current/sql/functions/window_functions) (read 2026-09-27)
- Duckle: [`NTile`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25)
- Ibis: [`NTile`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/analytic.py) (read 2026-09-27)
- RapidMiner Studio: [`Generate Batch`](https://docs.rapidminer.com/latest/studio/operators/blending/attributes/generation/generate_batch.html) (read 2026-09-27)