Select

Extracts a single field value from each object in an array, returning an array of those values.

Syntax

Select(array, fieldName)

Parameters

• array (array): The array of objects to extract from
• fieldName (string): The field name or nested path to extract (e.g., “status” or “address.city”)

Returns

• array: A new array containing the extracted field values from each object

Description

The Select function creates a new array by extracting the specified field from each object in the source array. This enables powerful composition with aggregate functions like Sum, Max, Min, and Avg.

The function supports nested field paths using dot notation, allowing you to extract deeply nested properties. Non-object elements result in null values at those positions. Objects missing the specified field also return null for that position.

Examples

Basic field extraction

var orders = [
    { "id": 1, "amount": 100, "customer": "Alice" },
    { "id": 2, "amount": 200, "customer": "Bob" },
    { "id": 3, "amount": 150, "customer": "Charlie" }
]

var amounts = Select(orders, "amount")
# amounts is [100, 200, 150]

var customers = Select(orders, "customer")
# customers is ["Alice", "Bob", "Charlie"]

Composing with aggregate functions

var orders = [
    { "amount": 100 },
    { "amount": 200 },
    { "amount": 150 }
]

var total = Sum(Select(orders, "amount"))
# total is 450

var highest = Max(Select(orders, "amount"))
# highest is 200

var average = Avg(Select(orders, "amount"))
# average is 150

Nested field extraction

var employees = [
    { "name": "Alice", "address": { "city": "New York", "zip": "10001" } },
    { "name": "Bob", "address": { "city": "Los Angeles", "zip": "90001" } },
    { "name": "Carol", "address": { "city": "Chicago", "zip": "60601" } }
]

var cities = Select(employees, "address.city")
# cities is ["New York", "Los Angeles", "Chicago"]

Getting unique values with Distinct

var products = [
    { "name": "Widget A", "category": "Electronics" },
    { "name": "Widget B", "category": "Clothing" },
    { "name": "Widget C", "category": "Electronics" },
    { "name": "Widget D", "category": "Home" },
    { "name": "Widget E", "category": "Clothing" }
]

var categories = Distinct(Select(products, "category"))
# categories is ["Electronics", "Clothing", "Home"]

Handling missing fields

var items = [
    { "a": 1, "b": 2 },
    { "a": 3 },
    { "b": 4 }
]

var aValues = Select(items, "a")
# aValues is [1, 3, null]

Handling non-object elements

var mixed = [
    { "x": 10 },
    "not an object",
    42,
    { "x": 20 },
    null
]

var xValues = Select(mixed, "x")
# xValues is [10, null, null, 20, null]

Notes

• The original array is never modified; a new array is always returned
• Non-object elements in the array result in null values at those positions
• Objects missing the specified field result in null values
• Nested paths traverse objects using dot notation (e.g., “user.profile.email”)
• Empty arrays return an empty array
• Can be chained with aggregate functions like Sum, Max, Min, Avg
• Can be chained with array functions like Distinct, Sort, Filter