查找对象数组中属性的最大值

我正在寻找一种非常快速,干净和有效的方法来获取以下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循环是唯一可行的方法吗？我热衷于某种方式使用Math.max.

要查找y对象的最大值array:

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

在对象数组中查找属性"X"具有最大值的对象

一种方法是使用Array reduce ..

const max = data.reduce(function(prev, current) {
    return (prev.y > current.y) ? prev : current
}) //returns object

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce http://caniuse.com/#search=reduce(IE99及以上版本)

如果您不需要支持IE(仅限Edge),或者可以使用诸如Babel之类的预编译器,则可以使用更简洁的语法.

const max = data.reduce((prev, current) => (prev.y > current.y) ? prev : current)

干净简洁的ES6(巴别塔)

const maxValueOfY = Math.max(...arrayToSearchIn.map(o => o.y), 0);

如果arrayToSearchIn为空,则第二个参数应确保默认值.

好吧,首先你应该解析JSON字符串,以便你可以轻松访问它的成员:

var arr = $.parseJSON(str);

使用该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);

或者作为一个单行:

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

我想逐步解释简洁的接受答案:

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('
objects: ' + JSON.stringify(objects) + '
');
document.write('
xValues: ' + JSON.stringify(xValues) + '
');
document.write('
xMax: ' + JSON.stringify(xMax) + '
');
document.write('
maxXObjects: ' + JSON.stringify(maxXObjects) + '
');
document.write('
maxXObject: ' + JSON.stringify(maxXObject) + '
');

var maxA = Math.max(...a.map(o=>o.y),a[0].y); // 33 chars time complexity: >O(2n)

var maxB = a.reduce((a,b)=>a.y>b.y?a:b).y;    // 30 chars time complexity:  O(n)

var maxC = a.sort((a,b)=>b.y-a.y)[0].y;       // 27 chars time complexity:  O(nlogn)

var maxA = Math.max(...a.map(o=>o.y),a[0].y); // 33 chars time complexity: >O(2n)

var maxB = a.reduce((a,b)=>a.y>b.y?a:b).y;    // 30 chars time complexity:  O(n)

var maxC = a.sort((a,b)=>b.y-a.y)[0].y;       // 27 chars time complexity:  O(nlogn)

var data = [
  { 'name': 'Vins', 'age': 27 },
  { 'name': 'Jan', 'age': 38 },
  { 'name': 'Alex', 'age': 80 },
  { 'name': 'Carl', 'age': 25 },
  { 'name': 'Digi', 'age': 40 }
];
var max = data.reduce(function (prev, current) {
   return (prev.age > current.age) ? prev : current
});
//output = {'name': 'Alex', 'age': 80}

_.maxBy(jsonSlice, 'y');

array.sort((a,b)=>a.y