Flip Method

The flip() method swaps the collection's keys with their corresponding values. For arrays, this means the values become the keys and the array indices become the values.

Basic Syntax

collect(items).flip()

Examples

Basic Usage

import { collect } from 'ts-collect'

// Simple key-value pairs
const data = collect({
  name: 'John',
  age: '30',
  city: 'New York'
})

console.log(data.flip().all())
// {
//   'John': 'name',
//   '30': 'age',
//   'New York': 'city'
// }

Working with Arrays

const array = collect(['a', 'b', 'c'])
console.log(array.flip().all())
// {
//   'a': 0,
//   'b': 1,
//   'c': 2
// }

Real-world Examples

Language Translations

interface Translations {
  [key: string]: string
}

const englishToSpanish = collect<Translations>({
  'hello': 'hola',
  'goodbye': 'adios',
  'thank you': 'gracias'
})

// Create Spanish to English translations
const spanishToEnglish = englishToSpanish.flip()
console.log(spanishToEnglish.all())
// {
//   'hola': 'hello',
//   'adios': 'goodbye',
//   'gracias': 'thank you'
// }

Status Code Mapping

interface StatusCodes {
  [key: string]: number
}

const httpStatusCodes = collect<StatusCodes>({
  'OK': 200,
  'Created': 201,
  'Not Found': 404,
  'Server Error': 500
})

// Create reverse lookup
const statusCodeMessages = httpStatusCodes.flip()
console.log(statusCodeMessages.all())
// {
//   '200': 'OK',
//   '201': 'Created',
//   '404': 'Not Found',
//   '500': 'Server Error'
// }

Advanced Usage

Configuration Mapping

interface ConfigMap {
  [key: string]: string
}

const environmentVariables = collect<ConfigMap>({
  DB_HOST: 'database.host',
  DB_PORT: 'database.port',
  DB_USER: 'database.username',
  DB_PASS: 'database.password'
})

// Create reverse mapping for configuration lookup
const configToEnvMap = environmentVariables.flip()
console.log(configToEnvMap.all())
// {
//   'database.host': 'DB_HOST',
//   'database.port': 'DB_PORT',
//   'database.username': 'DB_USER',
//   'database.password': 'DB_PASS'
// }

Role Permission Mapping

interface PermissionMap {
  [key: string]: string
}

const rolePermissions = collect<PermissionMap>({
  admin: 'all',
  editor: 'write',
  viewer: 'read'
})

// Create permission to role mapping
const permissionRoles = rolePermissions.flip()
console.log(permissionRoles.all())
// {
//   'all': 'admin',
//   'write': 'editor',
//   'read': 'viewer'
// }

Working with Duplicate Values

const dataWithDuplicates = collect({
  key1: 'value',
  key2: 'value',
  key3: 'unique'
})

// Note: When flipping, duplicate values will overwrite each other
console.log(dataWithDuplicates.flip().all())
// {
//   'value': 'key2',  // Only keeps the last occurrence
//   'unique': 'key3'
// }

Practical Applications

File Extension Mapping

interface MimeTypes {
  [key: string]: string
}

const mimeTypes = collect<MimeTypes>({
  html: 'text/html',
  css: 'text/css',
  js: 'application/javascript',
  json: 'application/json'
})

// Create reverse lookup for file type detection
const extensionLookup = mimeTypes.flip()
console.log(extensionLookup.all())
// {
//   'text/html': 'html',
//   'text/css': 'css',
//   'application/javascript': 'js',
//   'application/json': 'json'
// }

Type Safety

interface TypedMap {
  [key: string]: string | number
}

const typedData = collect<TypedMap>({
  id: 1,
  name: 'John',
  age: '30'
})

// TypeScript ensures type safety
const flipped = typedData.flip()
// The resulting types are automatically inferred

Return Value

Returns a new Collection instance with the keys and values flipped. Note that:

• For objects, the values become the new keys and the keys become the new values
• For arrays, the values become the keys and the indices become the values
• If there are duplicate values in the original collection, only the last occurrence will be preserved in the flipped result
• All values must be either strings or numbers to be valid as object keys