pickByMin / pickByMax

Select the item with the smallest or largest property value within a group.

Signature

pickByMin<ArrayName extends string, TPropName extends string>(
  arrayName: ArrayName,
  propertyName: keyof ArrayItem & string,
  outputProperty: TPropName
): PipelineBuilder</* type with outputProperty: ArrayItem | undefined */>

pickByMax<ArrayName extends string, TPropName extends string>(
  arrayName: ArrayName,
  propertyName: keyof ArrayItem & string,
  outputProperty: TPropName
): PipelineBuilder</* type with outputProperty: ArrayItem | undefined */>

Parameters

Parameter	Type	Description
arrayName	string	Name of the array to search
propertyName	string	Name of the property to compare
outputProperty	string	Name of the property to hold the selected item

Returns

A new PipelineBuilder with the selected item property added. Returns undefined for empty arrays.

Example: Latest Vote

Select the most recent vote by timestamp:

const builder = createPipeline<Vote>()
  .groupBy(["voterId", "candidateId"], "votes")
  .in("votes").pickByMax("items", "timestamp", "latestVote");

Result:

{
  key: "hash_Alice_X",
  value: {
    voterId: "Alice",
    candidateId: "X",
    latestVote: {
      voterId: "Alice",
      candidateId: "X",
      points: 8,
      timestamp: 1699999999  // the highest timestamp
    },
    items: [...]
  }
}

Example: Cheapest Product

Select the cheapest product in each category:

const builder = createPipeline<Product>()
  .groupBy(["category"], "products")
  .pickByMin("products", "price", "cheapestProduct");

Use Cases

• Latest by timestamp - pickByMax("items", "timestamp", "latest")
• Highest priority - pickByMin("items", "priority", "topPriority") (if lower = higher priority)
• Best rated - pickByMax("items", "rating", "topRated")
• Cheapest - pickByMin("items", "price", "cheapest")

Update Behavior

Add:

• Compare new item to current pick
• Update if new item wins
• O(1) operation

Remove:

• If removed item was the pick → rescan all items
• O(n) operation in worst case

Comparison Types

Supports both numeric and string comparisons:

// Numeric comparison
.pickByMax("items", "score", "highestScore")

// String comparison (lexicographic)
.pickByMin("items", "name", "firstAlphabetically")

See Also

• min / max - Get just the value, not the entire item