[GitHub] [incubator-echarts] wlc534 opened issue #9022: dataset提供渲染数据，怎么定制legend样式？

[GitHub]

### One-line summary [问题简述]
在使用dataset提供数据，按列的 key-value 形式。怎么定制legend样式？


### Version & Environment [版本及环境]

+ ECharts version [ECharts 版本]:v4.1.0
+ Browser version [浏览器类型和版本]:chrome 69
+ OS Version [操作系统类型和版本]:macOS 



### Expected behaviour [期望结果]

正常显示legend
![default](https://user-images.githubusercontent.com/26006959/45143099-d3e1f800-b1ec-11e8-9a81-1f49fb5a171a.png)



### ECharts option [ECharts配置项]
<!-- Copy and paste your 'echarts option' here. -->
<!-- [下方贴你的option，注意不要删掉下方 ```javascript 和 尾部的 ``` 字样。最好是我们能够直接运行的 
option。如何得到能运行的 option 参见上方的 guidelines for contributing] -->
```javascript
option = {
      title: {
                text: '多折线图'
            },
            tooltip: {
                trigger: 'axis'
            },
            legend: {
                
                data:[
                    {icon:'circle'},
                    {icon:'circle'},
                    {icon:'circle'},
                    {icon:'circle'},
                    {icon:'circle'},
                ]
            },
            dataset:{
                source:{
                    week:['周一','周二','周三','周四','周五','周六','周日'],
                    '邮件营销':[120, 132, 101, 134, 90, 230, 210],
                    '联盟广告':[220, 182, 191, 234, 290, 330, 310],
                    '视频广告':[150, 232, 201, 154, 190, 330, 410],
                    '直接访问':[320, 332, 301, 334, 390, 330, 320],
                    '搜索引擎':[820, 932, 901, 934, 1290, 1330, 1320],

                }

            },
            grid: {
                left: '3%',
                right: '4%',
                bottom: '3%',
                containLabel: true
            },
            toolbox: {
                feature: {
                    saveAsImage: {}
                }
            },
            xAxis: {
                type: 'category',
                boundaryGap: false,
               
            },
            yAxis: {
                type: 'value'
            },
            series: [
                {
                   type:'line'
                },
                {
                   type:'line'
                },
                {
                   type:'line'
                },
                {
                   type:'line'
                },
                {
                   type:'line'
                },
                
            ],
            color: [
                '#FF9C6E', '#FFC069', '#95DE64', '#5CDBD3', '#69C0FF', 
'#85A5FF', '#B37FEB', '#FF85C0'
            ]

}

```




### Other comments [其他信息]
<!-- For example: Screenshot or Online demo -->
<!-- [例如，截图或线上实例 (JSFiddle/JSBin/Codepen)] -->
是否可以考虑简化series、legend中配置，直接根据dataset自动生成。不然感觉冗余数据太多了。
legend: {
                data:['邮件营销','联盟广告','视频广告','直接访问','搜索引擎']
  
            },
series: [
                {
                   type:'line'
                },
                {
                   type:'line'
                },
                {
                   type:'line'
                },
                {
                   type:'line'
                },
                {
                   type:'line'
                },
                
            ],



[ Full content available at: 
https://github.com/apache/incubator-echarts/issues/9022 ]
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