D3 v4中多选择的简化方法

Question

我无法使reduce方法的工作ID为D3 v4。我收到reduce is not a function错误。怎么了？

var svg = d3.select('svg');

var dataSet = [10, 20, 30, 40];

var circle = svg.selectAll('circle')
    .data(dataSet)
    .enter()
    .append('circle')
    .attr("r",function(d){ return d })
    .attr("cx", function(d, i){ return i * 100 + 50 })
    .attr("cy",50)
    .attr("fill",'red')
   ;

var t=circle.reduce((total, circle) => total + circle.cx);
console.log(t)