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。
// Here is very simple way to go:
// Your DataSet.
let numberArray = [
{
"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
}
]
// 1. First create Array, containing all the value of Y
let result = numberArray.map((y) => y)
console.log(result) // >> [0.026572007,0.025057454,0.024530916,0.031004457]
// 2.
let maxValue = Math.max.apply(null, result)
console.log(maxValue) // >> 0.031004457
在对象数组中找到属性“Y”值最大的对象
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 (IE9及以上版本)
如果你不需要支持IE(只支持Edge),或者可以使用预编译器,比如Babel,你可以使用更简洁的语法。
const max = data.reduce((prev, current) => (prev.y > current.y) ? prev : current)
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 ()
非常简单
const array1 = [
{id: 1, val: 60},
{id: 2, val: 2},
{id: 3, val: 89},
{id: 4, val: 78}
];
const array2 = [1,6,8,79,45,21,65,85,32,654];
const max = array1.reduce((acc, item) => acc = acc > item.val ? acc : item.val, 0);
const max2 = array2.reduce((acc, item) => acc = acc > item ? acc : item, 0);
console.log(max);
console.log(max2);
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; }));