Question

我有一个看起来像这样的JSON文件：

编辑：我使用日期作为键，而不是以前键入的整数。

"2005-12-01": 120,
"2005-10-01": 32,

现在，我需要将第一列用作X轴，将另一列用作Y轴。在示例中，它们通过元素名称引用值，例如：

const line = d3.line()
    .x(d => x(d.date))
    .y(d => y(d.value));

在这里我不能做。

Answer 1

您必须将键映射到具有键/值对的对象数组，然后使用它来设置域并画线。

// The number of datapoints
var json = {
  "2005-12-01": 120,
  "2005-10-01": 32,
  "2005-08-01": 20,
  "2005-06-01": 123
};

var data = Object.keys(json).map(function (k) { 
  return {date: new Date(k), value: +json[k]};
});

其余代码与绘制简单折线图相同。

我使用问题中的JSON作为输入数据，创建了d3折线图示例的分支。（除数据映射外几乎无需更改任何行）

<!DOCTYPE html>
<meta charset="utf-8">

<style type="text/css">
.line {
    fill: none;
    stroke: #ffab00;
    stroke-width: 3;
}
</style>
<body>
</body>

<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

// 2. Use the margin convention practice 
var margin = {top: 50, right: 50, bottom: 50, left: 50}
  , width = window.innerWidth - margin.left - margin.right // Use the window's width 
  , height = window.innerHeight - margin.top - margin.bottom; // Use the window's height

// The number of datapoints
var json = {
"2005-12-01": 120,
"2005-10-01": 32,
"2005-08-01": 20,
"2005-06-01": 123
};

var data = Object.keys(json).map(function (k) { return {date: new Date(k), value: +json[k]};});

// 5. X scale will use the index of our data
var xScale = d3.scaleTime()
    .domain(d3.extent(data, d => d.date)) // input
    .range([0, width]); // output

// 6. Y scale will use the randomly generate number 
var yScale = d3.scaleLinear()
    .domain(d3.extent(data, d => d.value)) // input 
    .range([height, 0]); // output 

// 7. d3's line generator
var line = d3.line()
    .x(function(d, i) { return xScale(d.date); }) // set the x values for the line generator
    .y(function(d) { return yScale(d.value); }) // set the y values for the line generator 
    .curve(d3.curveMonotoneX) // apply smoothing to the line

// 1. Add the SVG to the page and employ #2
var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

// 3. Call the x axis in a group tag
svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(d3.axisBottom(xScale)); // Create an axis component with d3.axisBottom

// 4. Call the y axis in a group tag
svg.append("g")
    .attr("class", "y axis")
    .call(d3.axisLeft(yScale)); // Create an axis component with d3.axisLeft

// 9. Append the path, bind the data, and call the line generator 
svg.append("path")
    .datum(data) // 10. Binds data to the line 
    .attr("class", "line") // Assign a class for styling 
    .attr("d", line); // 11. Calls the line generator 

</script>

Answer 2

遍历JSON键并创建新对象

data = Object.keys(data).map(k => { return {x:+k, value: data[k]}; });

也许您需要对数组进行排序

data.sort( (a,b) => a.x - b.x );

var data = {"0": 120,
"1": 32,
"2": 234,
"3": 43};

data = Object.keys(data).map(k => { return {x:+k, value: data[k]}; });

console.log(data);

只有元组时如何从JSON将数据加载到D3图表

2 个答案: