Pipelines and Steps

This page describes the main steps available in aggregator-toy.

groupBy

Groups records by one or more keys and emits arrays of { key, value }.

.groupBy(["category", "region"], "items")

Input: Flat records with the specified key properties
Output: Nested structure with items grouped by unique key combinations

sum

Adds a numeric aggregate to each parent based on an array of children.

.sum("items", "price", "totalPrice")

Input: Array of items with a numeric property
Output: Parent enriched with sum property

count

Counts items in an array.

.count("items", "itemCount")

Input: Array of items
Output: Parent enriched with count property

min / max

Track the minimum or maximum value of a property within an array. These steps handle removals by recomputing from the stored items when needed.

.min("items", "price", "lowestPrice")
.max("items", "price", "highestPrice")

Input: Array of items with comparable property
Output: Parent enriched with min/max property

average

Tracks sum and count internally and exposes a single property.

.average("items", "price", "avgPrice")

Input: Array of items with numeric property
Output: Parent enriched with average property

pickByMin / pickByMax

Select the item with the smallest or largest property within a group and expose it as a property. This powers "latest vote by timestamp", "highest-priority job", or "lowest price in category" scenarios.

.pickByMax("items", "timestamp", "latestItem")
.pickByMin("items", "priority", "highestPriority")

Input: Array of items with comparable property
Output: Parent enriched with selected item reference

commutativeAggregate

Create custom aggregates with add and subtract operators.

.commutativeAggregate(
  "items",
  "customMetric",
  (acc, item) => (acc ?? 0) + item.value * item.weight,
  (acc, item) => acc - item.value * item.weight
)

Input: Array of items
Output: Parent enriched with custom aggregate property

in (scoping)

Creates a scoped builder that applies operations at the specified path depth.

.in("cities").sum("venues", "capacity", "totalCapacity")

defineProperty

Defines a computed property on each item.

.defineProperty("fullName", item => `${item.firstName} ${item.lastName}`)

dropProperty

Removes a property from each item.

.dropProperty("temporaryField")