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# Lodash Invert
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Lodash Invert provides the lodash invert and invertBy methods as standalone, modular utilities for creating objects composed of inverted keys and values. It includes both basic inversion (invert) and advanced grouping inversion (invertBy) functionality. This is a lightweight alternative to importing the entire lodash library when only inversion capabilities are needed.
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## Package Information
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- **Package Name**: lodash.invert
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- **Package Type**: npm
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- **Language**: JavaScript (ES5)
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- **Installation**: `npm install lodash.invert`
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- **License**: MIT
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## Core Imports
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```javascript
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var invert = require('lodash.invert');
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var invertBy = require('lodash.invert').invertBy;
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```
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For ES6/ESM environments:
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```javascript
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import invert, { invertBy } from 'lodash.invert';
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```
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## Basic Usage
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```javascript
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var invert = require('lodash.invert');
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var invertBy = require('lodash.invert').invertBy;
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// Basic inversion
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var object = { 'a': 1, 'b': 2, 'c': 1 };
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var result = invert(object);
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console.log(result);
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// => { '1': 'c', '2': 'b' }
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// Inversion with grouping
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var resultBy = invertBy(object);
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console.log(resultBy);
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// => { '1': ['a', 'c'], '2': ['b'] }
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// Real-world example: Creating lookup tables
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var statusCodes = { 'ok': 200, 'error': 500, 'notFound': 404 };
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var codeToStatus = invert(statusCodes);
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console.log(codeToStatus);
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// => { '200': 'ok', '500': 'error', '404': 'notFound' }
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```
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## Capabilities
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### Object Inversion
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Creates an object composed of the inverted keys and values of the input object. When duplicate values exist in the original object, subsequent values overwrite property assignments of previous values.
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```javascript { .api }
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/**
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 * Creates an object composed of the inverted keys and values of object.
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 * If object contains duplicate values, subsequent values overwrite property 
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 * assignments of previous values.
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 * 
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 * @param {Object} object The object to invert.
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 * @returns {Object} Returns the new inverted object.
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 */
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function invert(object);
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```
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### Object Inversion By Iteratee
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Creates an object composed of inverted keys and values, but uses an iteratee function to transform values before inversion. The inverted value of each inverted key is an array of keys responsible for generating that inverted value.
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```javascript { .api }
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/**
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 * This method is like invert except that the inverted object is generated
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 * from the results of running each element of object through iteratee.
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 * The corresponding inverted value of each inverted key is an array of keys
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 * responsible for generating the inverted value.
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 * 
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 * @param {Object} object The object to invert.
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 * @param {Function|Object|string} [iteratee=_.identity] The iteratee invoked per element.
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 * @returns {Object} Returns the new inverted object.
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 */
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function invertBy(object, iteratee);
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```
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**Parameters for invert:**
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- `object` (Object): The object to invert
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**Returns:**
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- (Object): Returns the new inverted object
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**Parameters for invertBy:**
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- `object` (Object): The object to invert
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- `[iteratee=_.identity]` (Function|Object|string): The iteratee invoked per element
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**Returns:**
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- (Object): Returns the new inverted object with arrays as values
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**Behavior:**
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- **invert**: Original object keys become values, original values become keys
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- **invert**: When duplicate values exist, the last key with that value overwrites previous assignments
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- **invertBy**: Groups keys by the transformed values, resulting in arrays of keys
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- **invertBy**: Uses iteratee function to transform values before grouping
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- Values are converted to strings when used as keys
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- Returns a new object (does not mutate the original)
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- Handles non-object inputs gracefully following lodash conventions
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**Usage Examples:**
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```javascript
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// Basic inversion
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var colors = { red: '#ff0000', blue: '#0000ff', green: '#00ff00' };
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invert(colors);
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// => { '#ff0000': 'red', '#0000ff': 'blue', '#00ff00': 'green' }
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// Duplicate values - last key wins
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var ratings = { good: 5, excellent: 5, poor: 1, bad: 1 };
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invert(ratings);
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// => { '5': 'excellent', '1': 'bad' }
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// invertBy with duplicate values - keys grouped in arrays
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invertBy(ratings);
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// => { '5': ['good', 'excellent'], '1': ['poor', 'bad'] }
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// invertBy with iteratee function
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var scores = { alice: 95, bob: 87, charlie: 95, dave: 87 };
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invertBy(scores, function(value) {
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  return 'grade-' + (value >= 90 ? 'A' : 'B');
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});
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// => { 'grade-A': ['alice', 'charlie'], 'grade-B': ['bob', 'dave'] }
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// Mixed value types
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var mixed = { a: 1, b: true, c: 'hello' };
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invert(mixed);
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// => { '1': 'a', 'true': 'b', 'hello': 'c' }
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// Empty object
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invert({});
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// => {}
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// Common use case: Creating reverse lookup maps
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var userRoles = { admin: 1, editor: 2, viewer: 3 };
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var roleIds = invert(userRoles);
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// Use roleIds['1'] to get 'admin', etc.
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```