Question

对于我正在尝试使用d3.js的图表，我需要设置轴的比例。图表的数据存储在如下结构的Json文件中：

    [{
    "id" : "AustraliaNewZealand" ,
    "year" : [1990,1992,1994,1993,1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010],
    "value":[477790,485825,487296,488885,502585,511718,526594,538967,550556,563572,577171,579126,591635,599216,604267,608954,615853,623685,618961,614920]
}, 
{
    "id":"CentralEurope",
    "year":[1990,1992,1994,1993,1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010],
    "value":[1548736,1334452,1313088,1283248,1314709,1360546,1343907,1285511,1237278,1251872,1244069,1233778,1284639,1297510,1317861,1359787,1396681,1361445,1278731,1343044]
}, 
{
    "id":"EasternEurope",
    "year":[1990,1992,1994,1993,1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010],
    "value":[4418516,3530464,3287987,2925644,2775181,2672238,2540975,2495036,2513372,2515375,2540796,2544848,2598148,2637682,2622241,2709974,2714204,2740248,2565213,2680226]
}, 
{
    "id":"NorthAmerica",
    "year":[1990,1992,1994,1993,1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010],
    "value":[6750754,6821412,6948829,7059001,7166869,7386971,7460485,7509719,7573562,7790060,7675762,7710685,7769154,7896824,7918461,7841686,7966277,7751508,7277713,7493948]
}, 
{
    "id":"WesternEurope",
    "year":[1990,1992,1994,1993,1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010],
    "value":[4365949,4290345,4222425,4221029,4264725,4353056,4290057,4310736,4251628,4260565,4306230,4278128,4333237,4337031,4305560,4267515,4209481,4125479,3841580,3924831
]
}]

我想做的是在嵌套的各种数组之间进行迭代，以获得年份和值的最小值和最大值，但我不知道如何获取这些值。我设法使用

获取单个数组的值

    var xScale = d3 .time.scale()
                .domain((d3.extent(dataset[0].year)))
                .range([margin*2, (width - margin)]);
var yScale = d3 .scale.linear()
                .domain([0, d3.max(dataset[0].value)])
                .range([(height - margin), margin]);

其中 dataset 是回调函数的标识符，但我想要的是获取所有数组之间的最小值和最大值（例如，min值在array3和数组中的最大值1）。我想我应该使用进行循环，但是我不知道应该把它放在哪里以及如何将其设置为查看所有数组，所以任何提示都会非常有用，谢谢！

Answer 1

如果我们在这里使用一些函数式编程而不是for循环，那将非常有趣：

d3.extent(dataset.reduce(function(a,b) { return a.concat(b.year) }, []))

您可以对值执行相同的操作。

Answer 2

如果您使用apply，数学函数min和max在这里非常有用：

function getMinMax(array, type) {
  var out = [];
  array.forEach(function(el) { return out.push.apply(out, el[type]); }, []);
  return { min: Math.min.apply(null, out), max: Math.max.apply(null, out) };
}

console.log(getMinMax(array, 'year')); // { min=1990, max=2010 }
console.log(getMinMax(array, 'value')); // { min=477790, max=7966277}

Fiddle

Answer 3

Javascript现在在Array上提供了一种flatMap方法，该方法既将数组数组展平为单个数组，又对每个元素应用转换函数：

var [min, max] = d3.extent(dataset.flatMap(d => d.value));

例如：

var input = [
  { id: "AustraliaNewZealand", value: [477790,485825,487296,488885,502585,511718,526594,538967,550556,563572,577171,579126,591635,599216,604267,608954,615853,623685,618961,614920] },
  { id: "CentralEurope",       value: [1548736,1334452,1313088,1283248,1314709,1360546,1343907,1285511,1237278,1251872,1244069,1233778,1284639,1297510,1317861,1359787,1396681,1361445,1278731,1343044] },
  { id: "EasternEurope",       value: [4418516,3530464,3287987,2925644,2775181,2672238,2540975,2495036,2513372,2515375,2540796,2544848,2598148,2637682,2622241,2709974,2714204,2740248,2565213,2680226] }
];

var [min, max] = d3.extent(input.flatMap(d => d.value));

console.log(min);
console.log(max);

<script src="https://d3js.org/d3-array.v2.min.js"></script>

在.json中查找最大值和最小值

3 个答案: