{{alias}}( [data,] [options] )
    Returns a sparkline up/down chart instance.

    Glyphs:

    | Value | Glyph |
    |:-----:|:-----:|
    |   1   |   ↑   |
    |   -1  |   ↓   |

    If provided any other value other than 1 or -1, the value is encoded as a
    missing value.

    The `data` argument takes precedence over the `data` option.

    Parameters
    ----------
    data: ArrayLike|ndarray (optional)
        Chart data.

    options: Object (optional)
        Options.

    options.autoRender: boolean (optional)
        Boolean indicating whether to re-render on a 'change' event. Default:
        false.

    options.bufferSize: integer|null (optional)
        Data buffer size. If provided, data is kept in a first-in first-out
        (FIFO) buffer which cannot exceed the buffer size. Default: +infinity.

    options.data: ArrayLike|ndarray (optional)
        Chart data.

    options.description: string (optional)
        Chart description.

    options.isDefined: Function (optional)
        An accessor function indicating whether a datum is defined.

    options.label: string (optional)
        Data label.

    Returns
    -------
    chart: UpDownChart
        Chart instance.

    chart.autoRender
        Rendering mode. If `true`, an instance renders on each 'change' event;
        otherwise, rendering must be triggered manually.

    chart.bufferSize
        Data buffer size.

    chart.description
        Chart description.

    chart.data
        Chart data.

    chart.label
        Data label.

    chart.isDefined( d, i )
        An accessor function which defines whether a datum is defined. This
        accessor is used to define how missing values are encoded. The default
        behavior is to ignore any values which are not 1 or -1.

    chart.render()
        Renders an up/down chart sparkline.

    Examples
    --------
    > var data = [ -1, 1, 1, 1, 1, -1, -1, 1 ];
    > var chart = new {{alias}}( data );
    > chart.render()
    '↓↑↑↑↑↓↓↑'

    See Also
    --------