{{alias}}( collection, [options,] indicator )
    Groups values according to an indicator function.

    When invoked, the indicator function is provided two arguments:

    - `value`: collection value
    - `index`: collection index

    The value returned by an indicator function should be a value which can be
    serialized as an object key.

    If provided an empty collection, the function returns an empty object.

    Parameters
    ----------
    collection: Array|TypedArray|Object
        Input collection to group. If provided an object, the object must be
        array-like (excluding strings and functions).

    options: Object (optional)
        Options.

    options.thisArg: any (optional)
        Execution context.

    options.returns: string (optional)
        If `values`, values are returned; if `indices`, indices are returned; if
        `*`, both indices and values are returned. Default: 'values'.

    indicator: Function
        Indicator function specifying which group an element in the input
        collection belongs to.

    Returns
    -------
    out: Object
        Group results.

    Examples
    --------
    > function indicator( v ) {
    ...     if ( v[ 0 ] === 'b' ) {
    ...         return 'b';
    ...     }
    ...     return 'other';
    ... };
    > var collection = [ 'beep', 'boop', 'foo', 'bar' ];
    > var out = {{alias}}( collection, indicator )
    { 'b': [ 'beep', 'boop', 'bar' ], 'other': [ 'foo' ] }

    // Output group results as indices:
    > var opts = { 'returns': 'indices' };
    > out = {{alias}}( collection, opts, indicator )
    { 'b': [ 0, 1, 3 ], 'other': [ 2 ] }

    // Output group results as index-value pairs:
    > opts = { 'returns': '*' };
    > out = {{alias}}( collection, opts, indicator )
    { 'b': [ [0, 'beep'], [1, 'boop'], [3, 'bar'] ], 'other': [ [2, 'foo' ] ] }

    See Also
    --------