问在D3.js树中在中心和不同节点之间绘制不同颜色的“笔画”

EN

var lines = svg.append("g").attr("class", "plot").selectAll("line");
        //define a d3 selection consisting of <line> elements
        //that are grouped within g.plot

    lines = lines.data(data);  
        //tell the selection to make room for every point in the data array

    lines.enter().append("line");
        //add one <line> element for every data point

    lines.each(function(d,i){
        //for each line in the selection, this function will be called
        //with d equal to the data point and i equal to the index
        //and "this" equal to the <line> element

        var value = d;
        //y-value for current point 
        //(we're just using the raw number from the array,
        //normally it would be something like d.y or d[1] )

        //find next point
        var next = i+1; //x-position (just using index #)
        var nextValue = data[i+1]; //y-position

        if (isNaN(nextValue)){
            // there is no next value,
            // so repeat this point as the end of line
            //(line will have zero length, but the marker will show up)
            next = i;
            nextValue = value;
        }

        d3.select(this) //select this particular <line> element
                        //so that we can use d3 methods

            //set coordinates:
            .attr( 
                {x1: xScale(i),
                 y1: yScale(value),
                 x2: xScale(next),
                 y2: yScale(nextValue)}
                )

            //Set styles for this individual line segment
            //e.g., based on whether value is increasing
            //or decreasing, we can set stroke colour red or black
            .style("stroke", ( (value > nextValue) ?
                              "red" :
                              "black" )
                  );
    });//end of "each" call

lines = lines.data(data);

lines.enter().append("line");

lines.attr("x1", function(d,i){return xScale(i);})
.attr("x2", function(d,i){
    return xScale( (i+1 == data.length)?i:i+1);
})
.attr("y1", function(d,i){return yScale(d);})
.attr("y2", function(d,i){
    return yScale( (i+1 == data.length)?
                  d:data[i+1]);
})
.style("stroke", function(d,i){
    return ( (d > data[i+1]) ?
             "red" : "black" )
    });