constructor (parent, chartGroup) {
        super();

        this._sliceCssClass = 'pie-slice';
        this._labelCssClass = 'pie-label';
        this._sliceGroupCssClass = 'pie-slice-group';
        this._labelGroupCssClass = 'pie-label-group';
        this._emptyCssClass = 'empty-chart';
        this._emptyTitle = 'empty';

        this._radius = undefined;
        this._givenRadius = undefined; // specified radius, if any
        this._innerRadius = 0;
        this._externalRadiusPadding = 0;


        this._g = undefined;
        this._cx = undefined;
        this._cy = undefined;
        this._minAngleForLabel = DEFAULT_MIN_ANGLE_FOR_LABEL;
        this._externalLabelRadius = undefined;
        this._drawPaths = false;

        this.colorAccessor(d => this.cappedKeyAccessor(d));

        this.title(d => `${this.cappedKeyAccessor(d)}: ${this.cappedValueAccessor(d)}`);

        this.label(d => this.cappedKeyAccessor(d));
        this.renderLabel(true);

        this.transitionDuration(350);
        this.transitionDelay(0);

        this.anchor(parent, chartGroup);
    }
Create a Pie Chart

@example
// create a pie chart under #chart-container1 element using the default global chart group
var chart1 = new PieChart('#chart-container1');
// create a pie chart under #chart-container2 element using chart group A
var chart2 = new PieChart('#chart-container2', 'chartGroupA');
@param {String|node|d3.selection} parent - Any valid
{@link https://github.com/d3/d3-selection/blob/master/README.md#select d3 single selector} specifying
a dom block element such as a div; or a dom element or d3 selection.
@param {String} [chartGroup] - The name of the chart group this chart instance should be placed in.
Interaction with a chart will only trigger events and redraws within the chart's group.