utils-object-inverse

Object Inverse

Inverts an object, such that keys are values and values are keys.

Installation

$ npm install utils-object-inverse

Usage

var invert = require( 'utils-object-inverse' );

invert( obj[, opts] )

Inverts an object, such that keys are values and values are keys.

var out = invert({
    'a': 'beep',
    'b': 'boop'
});
// returns {'beep':'a','boop':'b'}

The function accepts the following options:

• duplicates: boolean indicating whether to store keys mapped to duplicate values in arrays. Default: true.

By default, keys mapped to duplicate values are stored in arrays.

var out = invert({
    'a': 'beep',
    'b': 'beep'
});
// returns {'beep':['a','b']}

To not allow duplicates, set the duplicates option to false. The output key-value pair will be the key most recently inserted into the input object.

var obj = {};
obj.a = 'beep';
obj.b = 'boop';
obj.c = 'beep'; // inserted after `a`
 
var out = invert( obj, {
    'duplicates': false
});
// returns {'beep':'c','boop':'b'}

Notes

• Insertion order is not guaranteed, as object key enumeration is not specified according to the ECMAScript specification. In practice, however, most engines use insertion order to sort an object's keys, thus allowing for deterministic inversion.

• Beware when providing objects having values which are themselves objects. This implementation relies on native object serialization (#toString) when converting values to keys.

  var obj = {
      'a': [1,2,3],
      'b': {'c':'d'}
  };
   
  var out = invert( obj );
  // returns {'1,2,3':'a','[object Object]':'b'}

Examples

var invert = require( 'utils-object-inverse' );
 
var arr = new Array( 1000 ),
    len = arr.length,
    out,
    i;
 
// Create an array of random integers...
for ( i = 0; i < len; i++ ) {
    arr[ i ] = Math.round( Math.random()*100 );
}
// Invert the array to determine value frequency...
out = invert( arr );
keys = Object.keys( out );
len = keys.length;
for ( i = 0; i < len; i++ ) {
    out[ i ] = out[ i ].length;
}
console.dir( out );

To run the example code from the top-level application directory,

$ node ./examples/index.js

Tests

Unit

Unit tests use the Mocha test framework with Chai assertions. To run the tests, execute the following command in the top-level application directory:

$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

$ make view-cov

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License

MIT license.

Copyright

Copyright © 2015. Athan Reines.