💾arr.containsSubarray()

💾 程式

💡 祕技：下面的 valueIsInArraySequentially 用了一個內含參數 i 的 closure，讓每次測試「一個值是否在陣列中」，都從新的位置開始搜尋：

// ⭐️ 注意：函數的參數都是變數(var)
// intial value of `i` = 0  ￣￣￣￣￣￣⤵︎
(i => v => i = this.indexOf(v, i) + 1)(0)

簡直是太聰明了👍

when calling array.containsSubarray(), this === array

• replit

// 🔸 arr.containsSubarray()
Array.prototype.containsSubarray = function(subarray, orderIsRelevant=false) {
    
    // ⭐ closure with internal parameter `i`
    const valueIsInArraySequentially = (i => v => i = this.indexOf(v, i) + 1)(0);
    
    const valueIsInArray = (v => this.includes(v));
    const valuePassedTest = orderIsRelevant ? valueIsInArraySequentially : valueIsInArray;
    return subarray.every(valuePassedTest);
};

• valueIsInArraySequentially is equivalent to:

// closure (with internal variable `startFromIndex`)
const valueInArraySequentially = (()=>{
    // internal variable in clusure
    let startFromIndex = 0;
    // when calling `array.containsSubarray()`, `this === array`
    return (value) => startFromIndex = this.indexOf(value, startFromIndex) + 1;
})();

💈範例

💈範例：

⭐️ 注意：

當 orderIsRelevant 參數設為 false (預設值)，重複的值(如下面第三例)不管重複幾次，都會被當作有在陣列中(valueIsInArray)，依然會傳回 true❗️

// test array
const array = [12, 44, 22, 66, 222, 777, 22, 22, 22, 6, 77, 3];

[
    // order is relevant: NO  | YES
    // -----------------------------------
    [777, 22, 22],    // true | true
    [777, 22, 3],     // true | true
    [77, 77],         // true | false (true when order is irrelevant❗duplicate values neglected)
    [22, 44],         // true | false (false when order is relevant ⭐)
    
].forEach(arr => 
    console.log(
        array.containsSubarray(arr),            // order is irrelevant
        array.containsSubarray(arr, true)       // order IS relevant
    )
)

🗣 討論

• Javascript array contains/includes sub array ⭐️
• How to make function parameter constant in JavaScript?

📘 手冊

• Array.prototype.every()

  • Check if one array is a subset of another array
• Array.prototype.indexOf()

⬇️ 應用

• 不能補考名單

• 各班平均及前三名

• Google Apps Script app helpers.

👥 相關

• tips

• arrow function doesn't have its own this.