我正在寻找一个非常快速,干净和有效的方法来获得以下JSON切片中的最大“y”值:

[
  {
    "x": "8/11/2009",
    "y": 0.026572007
  },
  {
    "x": "8/12/2009",
    "y": 0.025057454
  },
  {
    "x": "8/13/2009",
    "y": 0.024530916
  },
  {
    "x": "8/14/2009",
    "y": 0.031004457
  }
]

for循环是唯一的方法吗?我很喜欢用Math.max。


当前回答

又快又脏:

Object.defineProperty (Array.prototype“分钟”, { 价值:函数(f) { F = F || (v => v); 返回。Reduce ((a, b) => (f(a) < f(b)) ?A: b); } }); Object.defineProperty (Array.prototype‘麦克斯’, { 价值:函数(f) { F = F || (v => v); 返回。Reduce ((a, b) => (f(a) > f(b)) ?A: b); } }); console.log ([1, 2, 3] .max ()); console.log([1, 2, 3]。Max (x => x*(4-x))); console.log ([1, 2, 3] .min ()); console.log([1, 2, 3]。Min (x => x*(4-x)));

其他回答

如果你(或这里的某人)可以自由使用lodash实用程序库,它有一个maxBy函数,在你的情况下会非常方便。

因此你可以用as such:

_.maxBy(jsonSlice, 'y');

求数组中所有对象的y的最大值:

    Math.max.apply(Math, array.map(function(o) { return o.y; }))

或者在更现代的JavaScript中:

    Math.max(...array.map(o => o.y))

ES6解决方案

Math.max(…array.map(函数(o){返回o.y;}))

详情见https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/max

我想一步一步地解释这个简短的公认答案:

var objects = [{ x: 3 }, { x: 1 }, { x: 2 }]; // array.map lets you extract an array of attribute values var xValues = objects.map(function(o) { return o.x; }); // es6 xValues = Array.from(objects, o => o.x); // function.apply lets you expand an array argument as individual arguments // So the following is equivalent to Math.max(3, 1, 2) // The first argument is "this" but since Math.max doesn't need it, null is fine var xMax = Math.max.apply(null, xValues); // es6 xMax = Math.max(...xValues); // Finally, to find the object that has the maximum x value (note that result is array): var maxXObjects = objects.filter(function(o) { return o.x === xMax; }); // Altogether xMax = Math.max.apply(null, objects.map(function(o) { return o.x; })); var maxXObject = objects.filter(function(o) { return o.x === xMax; })[0]; // es6 xMax = Math.max(...Array.from(objects, o => o.x)); maxXObject = objects.find(o => o.x === xMax); document.write('<p>objects: ' + JSON.stringify(objects) + '</p>'); document.write('<p>xValues: ' + JSON.stringify(xValues) + '</p>'); document.write('<p>xMax: ' + JSON.stringify(xMax) + '</p>'); document.write('<p>maxXObjects: ' + JSON.stringify(maxXObjects) + '</p>'); document.write('<p>maxXObject: ' + JSON.stringify(maxXObject) + '</p>');

进一步的信息:

Math.max.apply () Array.prototype.map () Array.from () Function.prototype.apply () Array.prototype.filter () Array.prototype.find ()

首先,你应该解析JSON字符串,这样你就可以很容易地访问它的成员:

var arr = $.parseJSON(str);

使用map方法提取值:

arr = $.map(arr, function(o){ return o.y; });

然后你可以在max方法中使用数组:

var highest = Math.max.apply(this,arr);

或者作为一行语句:

var highest = Math.max.apply(this,$.map($.parseJSON(str), function(o){ return o.y; }));