Mangler.index()

Builds a lookup object using object properties or a custom key generator.

Mangler.index(array, generator[, delimiter])

Parameter	Type	Default	Description
array	Array Mangler		An array of objects to build the index for. Passing a mangler object will build an index from its items.
generator	String Array.String Function		If a string or array of strings is passed, the keys used to build the index will be read by Mangler.getPath() from each object. If a function is passed, it will be called for each item with parameters function(index, item), and it must return either a string to be used as a key, or false to leave the item out of the index.
delimiter	String	`'	'`

Returns

Returns the generated lookup object.

---

Indexing a property

This example will build an index on the id property to easily find the object to change.

data = [
	{ id: '001', name: 'Mr Smith' },
	{ id: '002', name: 'John' },
	{ id: '003', name: 'Jack' }
];

lookup = Mangler.index(data, 'id');

/*
	lookup = {
		'001': { id: '001', name: 'Mr Smith' },
		'002': { id: '002', name: 'John' },
		'003': { id: '003', name: 'Jack' }
	}
*/

Now it is easy to change the name of a record by its id:

lookup['002'].name = 'Bill';

Because of the preserved object references, the name was changed in the original data as well, and its structure is untouched.

This method is useful if you use the returned lookup object several times. In case you only do a single query, consider using Mangler.first() instead:

Mangler.first(data, { id: '002' }).name = 'Bill';

Index from multiple fields

You can pass and array of strings to build a composite key:

data = [
	{ part1: 'A', part2: '001', name: 'Mr Smith' },
	{ part1: 'B', part2: '001', name: 'John' },
	{ part1: 'B', part2: '002', name: 'Jack' }
];

lookup = Mangler.index(data, ['part1', 'part2']);

/*
	lookup = {
		'A|001': { part1: 'A', part2: '001', name: 'Mr Smith' },
		'B|001': { part1: 'B', part2: '001', name: 'John' },
		'B|002': { part1: 'B', part2: '002', name: 'Jack' }
	}
*/

To change the default delimiter, pass a third parameter:

lookup = Mangler.index(data, ['part1', 'part2'], '-');

/*
	lookup = {
		'A-001': { part1: 'A', part2: '001', name: 'Mr Smith' },
		'B-001': { part1: 'B', part2: '001', name: 'John' },
		'B-002': { part1: 'B', part2: '002', name: 'Jack' }
	}
*/

Custom index

To generate the index keys yourself, or to filter the items that goes into the index, you can use a key generator function as the generator parameter. The following example filters out cats and builds a unique ID for dogs:

data = [
	{ type: 'dog', name: 'Fred' },
	{ type: 'cat', name: 'Fluffy' },
	{ type: 'dog', name: 'Oscar' }
];

dogs = Mangler.index(data, function(i, v) {
	return v.type === 'dog' ? v.type.toUpperCase() + i : false;
});

/*
	dogs = {
		'DOG0': { type: 'dog', name: 'Fred' },
		'DOG2': { type: 'dog', name: 'Oscar' }
	}
*/