.reduce（）関数を使用して要素にアクセスする

Question

.reduce()関数がどのように機能しているかを理解しようとしています。 だから、私たちは購入のアレイを持っています。各購入はオブジェクトです。

const purchases = [{"owner":"Barry","price":103}, 
{"owner":"Bob","price":75}, 
{"owner":"Bob","price":73},{"owner":"Barry","price":57}, 
{"owner":"Barry","price":128}, 
{"owner":"Bob","price":119},{"owner":"Barry","price":133}, 
{"owner":"Barry","price":27}, 
{"owner":"Barry","price":138},{"owner":"Bob","price":68}, 
{"owner":"Bob","price":50}, 
{"owner":"Barry","price":9},{"owner":"Bob","price":123}, 
{"owner":"Bob","price":135}, 
{"owner":"Barry","price":30},{"owner":"Barry","price":129}, 
{"owner":"Barry","price":38}, 
{"owner":"Bob","price":133},{"owner":"Barry","price":109}, 
{"owner":"Bob","price":115}] 

私は.reduce（）関数を使用してボブのためのすべての購入を蓄積しようとしています。私のコードは以下の通りです：

let bobsTotal = purchases.reduce(el => { 
    if (el["owner"] === "Barry") {return el["price"]} 
}) 

「価格」プロパティへのアクセス方法はわかりません。

Answer 1

ときArray.prototype.reduce(function, accumulator)：あなたは、本質的にaccumulatorを更新するarrayに各object上functionを反復しています。

ここで、functionは、(accumulator, object, index, array) => (accumulator)の形式をとります。

詳細はMozilla documentation referenceをご覧ください。

具体的な例については、以下のコードを参照してください。ボブのための

// Purchases. 
 
const purchases = [ 
 
    {"owner":"Barry","price":103}, 
 
    {"owner":"Bob","price":75}, 
 
    {"owner":"Bob","price":73}, 
 
    {"owner":"Barry","price":57}, 
 
    {"owner":"Barry","price":128}, 
 
    {"owner":"Bob","price":119}, 
 
    {"owner":"Barry","price":133}, 
 
    {"owner":"Barry","price":27}, 
 
    {"owner":"Barry","price":138}, 
 
    {"owner":"Bob","price":68}, 
 
    {"owner":"Bob","price":50}, 
 
    {"owner":"Barry","price":9}, 
 
    {"owner":"Bob","price":123}, 
 
    {"owner":"Bob","price":135}, 
 
    {"owner":"Barry","price":30}, 
 
    {"owner":"Barry","price":129}, 
 
    {"owner":"Barry","price":38}, 
 
    {"owner":"Bob","price":133}, 
 
    {"owner":"Barry","price":109}, 
 
    {"owner":"Bob","price":115} 
 
] 
 

 
// Total Bob. 
 
const totalBob = purchases.reduce((total, purchase) => {  
 
    if (purchase.owner == 'Bob') total += purchase.price // Owner == Bob. 
 
    return total  
 
}, 0) 
 

 
// Log. 
 
console.log(totalBob)