src/charts/grouped-bar.js
function verticalBarsTween(d) {
            let node = d3Selection.select(this),
                i = d3Interpolate.interpolateRound(0, chartHeight - yScale(getValue(d))),
                y = d3Interpolate.interpolateRound(chartHeight, yScale(getValue(d))),
                j = d3Interpolate.interpolateNumber(0, 1);

            return function (t) {
                node.attr('y', y(t))
                    .attr('height', i(t)).style('opacity', j(t));
            }
        }
function verticalBarsTween(d) {
            let node = d3Selection.select(this),
                i = d3Interpolate.interpolateRound(0, chartHeight - yScale(getValue(d))),
                y = d3Interpolate.interpolateRound(chartHeight, yScale(getValue(d))),
                j = d3Interpolate.interpolateNumber(0, 1);

            return function (t) {
                node.attr('y', y(t))
                    .attr('height', i(t)).style('opacity', j(t));
            }
        }
function verticalBarsTween ( d ) { let node = d3Selection . select ( this ) , i = d3Interpolate . interpolateRound ( 0 , chartHeight - yScale ( getValue ( d ) ) ) , y = d3Interpolate . interpolateRound ( chartHeight , yScale ( getValue ( d ) ) ) , j = d3Interpolate . interpolateNumber ( 0 , 1 ) ; return function ( t ) { node . attr ( 'y' , y ( t ) ) . attr ( 'height' , i ( t ) ) . style ( 'opacity' , j ( t ) ) ; } }
Animation tween of vertical bars
@param  {obj} d data of bar
@return {void}
Animation tween of vertical bars