d3js:如何选择组的第n个元素？

Question

我创建了一个包含9个元素(圆圈)的组,例如:

// JS
var data=[ 1,2,3,4,5,6,7,8,9 ];
var svg = d3.select("body").append("svg");
var circles = svg.append("g").attr("id", "groupOfCircles")
    .selectAll("circle")
        .data(data)
    .enter().append("circle")
        .attr("cx", function(d){ return d*20;})
        .attr("cy", function(d){ return d*10;})
        .attr("r" , function(d){ return d;})
        .attr("fill","green");

//xml
<svg>
    <g id="groupOfCircles">
        <circle cx="20" cy="10" r="1" fill="green"></circle>
        <circle cx="40" cy="20" r="2" fill="green"></circle>
        <circle cx="60" cy="30" r="3" fill="green"></circle>
        <circle cx="80" cy="40" r="4" fill="green"></circle>
        <circle cx="100" cy="50" r="5" fill="green"></circle>
        <circle cx="120" cy="60" r="6" fill="green"></circle>
        <circle cx="140" cy="70" r="7" fill="green"></circle>
        <circle cx="160" cy="80" r="8" fill="green"></circle>
        <circle cx="180" cy="90" r="9" fill="green"></circle>
    </g>
</svg>

但是如何groupOfCircles在不知道圆圈的id或属性值的情况下选择组的第n个元素(即:第3个圆圈)？

稍后我将通过for循环遍历所有元素,并将每个元素着色一秒钟.

---

注意:我尝试过如下操作:

  circles[3].attr("fill","red") // not working
  d3.select("#groupOfCircles:nth-child(3)").attr("fill","red")  // not working
  ..

Answer 1

选择器需要circle:nth-child(3)- child表示元素是第n个子元素,而不是选择元素的第n个子元素(参见此处).

你也可以使用:

    // JS
    var data=[ 1,2,3,4,5,6,7,8,9 ];
    var svg = d3.select("body").append("svg");
    var circles = svg.append("g").attr("id", "groupOfCircles")
        .selectAll("circle")
            .data(data)
        .enter().append("circle")
            .attr("cx", function(d){ return d*20;})
            .attr("cy", function(d){ return d*10;})
            .attr("r" , function(d){ return d;})
            .attr("fill","green");
    
    d3.select("circle:nth-child(3)").attr("fill","red"); // <== CSS selector (DOM)
    d3.select(circles[0][4]).attr("fill","blue"); // <== D3 selector (node)

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>

Answer 2

d3 v4现在支持使用selection .nodes() 返回此selection的所有元素的数组。然后，我们可以通过 d3.select( selection .nodes()[ n ]).attr( something )改变第n个元素的属性

// JS
var data=[ 1,2,3,4,5,6,7,8,9 ];
var svg = d3.select("body").append("svg");
var circles = svg.append("g").attr("id", "groupOfCircles")
    .selectAll("circle")
        .data(data)
    .enter().append("circle")
        .attr("cx", function(d){ return d*20;})
        .attr("cy", function(d){ return d*10;})
        .attr("r" , function(d){ return d;})
        .attr("fill","green");

circleElements = circles.nodes(); // <== Get all circle elements
d3.select(circleElements[6]).attr("fill","red");

<script src="https://d3js.org/d3.v4.min.js"></script>