Project

Creates new objects containing only the specified fields from each object in the source array.

Syntax

Project(array, fieldNames)

Parameters

array (array): The array of objects to project from
fieldNames (array): An array of field names or nested paths to include in the projected objects

Returns

array: A new array of objects containing only the specified fields

Description

The Project function creates a new array where each object contains only the fields specified in the fieldNames array. This is similar to a SQL SELECT statement that picks specific columns.

The function supports nested field paths using dot notation. For nested paths like “address.city”, the leaf field name (“city”) is used as the key in the projected object.

Non-object elements in the source array are skipped. Missing fields result in null values in the projected objects.

Examples

Basic projection

var employees = [
    { "id": 1, "name": "Alice", "salary": 50000, "ssn": "123-45-6789" },
    { "id": 2, "name": "Bob", "salary": 60000, "ssn": "987-65-4321" }
]

# Project only public-safe fields
var publicInfo = Project(employees, ["id", "name"])
# publicInfo is [
#   { "id": 1, "name": "Alice" },
#   { "id": 2, "name": "Bob" }
# ]

Projection with nested fields

var customers = [
    { "id": 1, "name": "Alice", "address": { "city": "NYC", "zip": "10001" } },
    { "id": 2, "name": "Bob", "address": { "city": "LA", "zip": "90001" } }
]

var summary = Project(customers, ["name", "address.city"])
# summary is [
#   { "name": "Alice", "city": "NYC" },
#   { "name": "Bob", "city": "LA" }
# ]

Data sanitization

var userData = [
    { "username": "alice", "email": "alice@example.com", "password": "secret123", "apiKey": "key123" },
    { "username": "bob", "email": "bob@example.com", "password": "secret456", "apiKey": "key456" }
]

# Remove sensitive fields before sending to client
var safeData = Project(userData, ["username", "email"])
# safeData is [
#   { "username": "alice", "email": "alice@example.com" },
#   { "username": "bob", "email": "bob@example.com" }
# ]

Creating summary views

var orders = [
    { "orderId": "A001", "customer": "Alice", "total": 150, "items": [...], "shippingAddress": {...} },
    { "orderId": "A002", "customer": "Bob", "total": 200, "items": [...], "shippingAddress": {...} }
]

var orderSummary = Project(orders, ["orderId", "customer", "total"])
# orderSummary is [
#   { "orderId": "A001", "customer": "Alice", "total": 150 },
#   { "orderId": "A002", "customer": "Bob", "total": 200 }
# ]

Handling missing fields

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

var projected = Project(items, ["a", "b"])
# projected is [
#   { "a": 1, "b": 2 },
#   { "a": 3, "b": null },
#   { "a": null, "b": 4 }
# ]

Handling non-object elements

var mixed = [
    { "x": 1, "y": 2 },
    "string",
    null,
    { "x": 3, "y": 4 }
]

var projected = Project(mixed, ["x"])
# projected is [
#   { "x": 1 },
#   { "x": 3 }
# ]
# Non-object elements are skipped

Empty field list

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

var empty = Project(items, [])
# empty is [{}, {}]
# Objects with no fields

Notes

The original array is never modified; a new array is always returned
Non-object elements in the source array are skipped entirely
Missing fields result in null values in the projected objects
For nested paths (e.g., “address.city”), the leaf name (“city”) is used as the property key
Nested paths traverse objects using dot notation
Empty arrays return an empty array
An empty field list results in empty objects for each source object
Non-string values in the fieldNames array are ignored