のJavaScriptコード（）

Question

var developers = [ 
    { name: "Joe", age: 23 ,overallLevel: "high"}, 
    { name: "Sue", age: 28 ,overallLevel: "advanced" }, 
    { name: "Jon", age: 32 ,overallLevel: "high" }, 
    { name: "Bob", age: 24 ,overallLevel: "high" }, 
    { name: "Bob", age: 20 ,overallLevel: "advanced" } 
] 

は ）（array.reduceを用いて述べたアレイにoverallLevelのカウントが必要[高：3、高度：2]

Answer 1

あなたはオブジェクトでそれらを数えることができます。

var developers = [{ name: "Joe", age: 23, overallLevel: "high" }, { name: "Sue", age: 28, overallLevel: "advanced" }, { name: "Jon", age: 32, overallLevel: "high" }, { name: "Bob", age: 24, overallLevel: "high" }, { name: "Bob", age: 20, overallLevel: "advanced" }], 
 
    overallLevel = developers.reduce(function (r, a) { 
 
     r[a.overallLevel] = (r[a.overallLevel] || 0) + 1; 
 
     return r; 
 
    }, {}); 
 

 
console.log(overallLevel);

Answer 2

（あなたがことを行うにはarray.reduce()を必要としない）、これを試してみてください：

var 
 
    i, 
 
    count = {high: 0, advanced: 0}, 
 
    developers = [ 
 
    { name: "Joe", age: 23 ,overallLevel: "high"}, 
 
    { name: "Sue", age: 28 ,overallLevel: "advanced" }, 
 
    { name: "Jon", age: 32 ,overallLevel: "high" }, 
 
    { name: "Bob", age: 24 ,overallLevel: "high" }, 
 
    { name: "Bob", age: 20 ,overallLevel: "advanced" } 
 
    ]; 
 

 
for (i in developers) { 
 

 
    count[developers[i].overallLevel]++; 
 
} 
 

 
alert(JSON.stringify(count)); // Object { high=3, advanced=2}