function group( collection, options, groups ) {
	var opts;
	var err;
	var g;
	if ( !isCollection( collection ) ) {
		throw new TypeError( format( 'invalid argument. First argument must be a collection. Value: `%s`.', collection ) );
	}
	opts = {
		'returns': 'values'
	};
	if ( arguments.length === 2 ) {
		g = options;
	} else {
		err = validate( opts, options );
		if ( err ) {
			throw err;
		}
		g = groups;
	}
	if ( !isCollection( g ) ) {
		throw new TypeError( format( 'invalid argument. Last argument must be a collection. Value: `%s`.', g ) );
	}
	if ( collection.length !== g.length ) {
		throw new RangeError( 'invalid arguments. First and last arguments must be the same length.' );
	}
	if ( opts.returns === 'values' ) {
		return returnValues( collection, g );
	}
	if ( opts.returns === 'indices' ) {
		return returnIndices( collection, g );
	}
	return returnPairs( collection, g );
}
Groups values as arrays associated with distinct keys.

@param {Collection} collection - collection to group
@param {Options} [options] - function options
@param {string} [options.returns="values"] - if `values`, values are returned; if `indices`, indices are returned; if `*`, both indices and values are returned
@param {Collection} groups - collection defining which group an element in the input collection belongs to
@throws {TypeError} first argument must be a collection
@throws {TypeError} options argument must be an object
@throws {TypeError} last argument must be a collection
@throws {TypeError} must provide valid options
@throws {RangeError} first and last arguments must be the same length
@returns {Object} group results

@example
var arr = [ 'beep', 'boop', 'foo', 'bar' ];
var groups = [ 'b', 'b', 'f', 'b' ];

var out = group( arr, groups );
// returns { 'b': [ 'beep', 'boop', 'bar' ], 'f': [ 'foo' ] }

@example
var arr = [ 'beep', 'boop', 'foo', 'bar' ];
var groups = [ 'b', 'b', 'f', 'b' ];

var opts = {
    'returns': 'indices'
};

var out = group( arr, opts, groups );
// returns { 'b': [ 0, 1, 3 ], 'f': [ 2 ] }

@example
var arr = [ 'beep', 'boop', 'foo', 'bar' ];
var groups = [ 'b', 'b', 'f', 'b' ];

var opts = {
    'returns': '*'
};

var out = group( arr, opts, groups );
// returns { 'b': [ [ 0, 'beep' ], [ 1, 'boop' ], [ 3, 'bar' ] ], 'f': [ [ 2, 'foo' ] ] }