您正在混合两种不同的方法，一种是将数据绑定到行，另一种是将数据传递到行函数。任何一个都可以工作（只要你只有一行），但如果你想摆脱你的if / else结构，你仍然需要分离语句处理从语句更新中添加元素

You're mixing up two different approaches, one binding data to the line and the other just passing the data to the line function. Either one could work (so long as you only have the one line), but if you want to get rid of your if/else construct you're still going to need to separate the statements handling entering/appending the element from the statements updating it.

选项1 （不绑定数据，只需调用函数）：

Option 1 (don't bind data, just call the function):

var linegraph = channelGroup.select('path');

if ( linegraph.empty() ) {
     //handle the entering data
     linegraph = channelGroup.append('path')
                      .attr("class", "line")
                      .style("stroke", channel.Color);
}

linegraph
        .transition()
        .ease("linear")
        .duration(animChart / 2)
        .attr('d', line(channel.DataRows));

选项2 （使用数据加入）：

var linegraph = channelGroup.selectAll("path")
        .data([channel.DataRows]);

linegraph.enter().append('path')
                 .attr("class", "line");

linegraph
        .transition()
        .ease("linear")
        .duration(animChart / 2)
        .attr("d", line); //This is slightly more efficient than
                          //function (d) { return line(d); }
                          //and does the exact same thing.
                          //d3 sees that `line` is a function, and 
                          //therefore calls it with the data as the 
                          //first parameter.