迭代一组对象

Question

I want to iterate over an array of objects in order to get the oldest person and the youngest person. How could I get that? It looks like an easy task, but there is no way I can get the ages with simple for each loop. Any ideas?

var p = [
    { name : "Billy", age : 5 },
    { name : "Lucy", age : 31 },
    { name : "Jonny", age : 11 },
    { name : "Wolfgang", age : 78 },
    { name : "Robert", age : 23 }
];

I have seen this but it didn't help me in understanding the problem.

Answer 1

Simple for loop

var high = 0,
    low;

//Start at 0 index, iterate until the array length, iterate by 1
for (var i = 0; i < p.length; i++) {
    //checking high
    if (p[i].age > high)
        high = p[i].age;

    //checking low
    if (p[i].age < low || low == null)
        low = p[i].age;
}

Answer 2

You can use a for in loop to solve this. The only thing you need to remember that the loop will give you only the index. Therefore you need to access the original object.

A possible solution is:

var maxPerson = p[0];

for(var i in p) {
    if (p[i].age > maxPerson.age)
        maxPerson = p[i];
}

Answer 3

To iterate over array in JavaScript, you use .forEach .

p.forEach(function(person){
    console.log(person.name + ' is ' + person.age + ' years old.');
});

Note that .forEach is not supported in IE 8 and below. You can use es5-shim to add that functionality to old browsers, or use jQuery each if you already use jQuery anyway.

Now to get the oldest and the youngest we need to store the best choices as we loop over the list ( jsFiddle ):

var oldest = p[0];
var youngest = p[0];
p.forEach(function(person){
    if (oldest.age < person.age) { oldest = person; }
    if (person.age < youngest.age) { youngest = person; }
});

In the end, oldest and youngest will contain the appropriate objects.

Answer 4

如果您只想检索最旧和最年轻的两个对象，那么最简单的方法是根据年龄按升序或降序对数组进行排序 ，然后获取结果数组的第一个和最后一个元素。

Answer 5

Using sort ( mdn doc ) will work in every browser :

p.sort(function (a, b) {
    return a.age - b.age;
});

var youngest = p[0];
var oldest = p[p.length - 1];

Be careful however, sort modifies the original array. You may clone it in order to bypass this issue :

var clone = [].concat(p).sort(/* compare function */);
var youngest = clone[0];
var oldest = clone[clone.length - 1];