在一個屬性上對 object 數組進行分組，同時計算 javascript 中另一個屬性的值

Question

我需要計算一個屬性的特定值的出現次數，按另一個屬性的值分組。 我有工作代碼，但我覺得它可以更通用地完成。

首先，我有兩個常量 arrays。我有一個與年份有關的常量和一個與值的不同可能性有關的常量。 第三個數組 (myArray) 是由 REST 調用形成的數組。

const properties = ["a", "b", "c"]
const years = [2015, 2016, 2017, 2018]

let myArray = [
    { date: 2015, prop1: "a" },
    { date: 2015, prop1: "b" },
    { date: 2016, prop1: "b" },
    { date: 2016, prop1: "a" },
    { date: 2016, prop1: "c" },
    { date: 2017, prop1: "b" },
    { date: 2017, prop1: "a" },
    { date: 2017, prop1: "a" },
    { date: 2017, prop1: "b" },
    { date: 2017, prop1: "b" },
    { date: 2018, prop1: "c" },
    { date: 2018, prop1: "b" },

]

接下來我有我的 function。它看起來像這樣。

function doClick() {
    let countArray = [];
    let counta = 0;
    let countb = 0;
    let countc = 0;

    for (let i = 0; i < years.length; i++) {
        let currentYear = years[i]
        for (let x = 0; x < properties.length; x++) {
            let currentProperty = properties[x];
            for (let z = 0; z < myArray.length; z++) {
                if (myArray[z].date === currentYear && myArray[z].prop1 === currentProperty) {
                    switch (currentProperty) {
                        case "a":
                            counta++;
                            break;
                        case "b":
                            countb++;
                            break;
                        case "c":
                            countc++;
                            break;
                    }
                }
            }
        }
        let obj = {
            'year': currentYear,
            'a': counta,
            'b': countb,
            'c': countc
        }
        countArray.push(obj)
        counta = 0;
        countb = 0;
        countc = 0;
    }
    console.log(countArray)
}

這會記錄一個我可以使用的數組。

0: {year: 2015, a: 1, b: 1, c: 0}
1: {year: 2016, a: 1, b: 1, c: 1}
2: {year: 2017, a: 2, b: 3, c: 0}
3: {year: 2018, a: 0, b: 1, c: 1}

但是常量數組屬性實際上要大得多。 所以我想擺脫 switch 語句和 lets counta、countb 和 countc 中的硬編碼情況，並使其更加靈活。

那么任何人都可以幫助我更好地獲得這段代碼嗎？

謝謝！

Answer 1

您可以將 object 分組，並將prop1作為屬性訪問器來增加計數。

 const properties = ["a", "b", "c"], years = [2015, 2016, 2017, 2018], data = [{ date: 2015, prop1: "a" }, { date: 2015, prop1: "b" }, { date: 2016, prop1: "b" }, { date: 2016, prop1: "a" }, { date: 2016, prop1: "c" }, { date: 2017, prop1: "b" }, { date: 2017, prop1: "a" }, { date: 2017, prop1: "a" }, { date: 2017, prop1: "b" }, { date: 2017, prop1: "b" }, { date: 2018, prop1: "c" }, { date: 2018, prop1: "b" }], empty = Object.fromEntries(properties.map(k => [k, 0])), result = Object.values(data.reduce( (r, { date, prop1 }) => { r[date][prop1]++; return r; }, Object.fromEntries(years.map(year => [year, { year, ...empty }]))) ); console.log(result);

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Answer 2

您不需要定義 2 個常量。 你可以查看我下面的演示：

 let myArray = [ { date: 2015, prop1: "a" }, { date: 2015, prop1: "b" }, { date: 2016, prop1: "b" }, { date: 2016, prop1: "a" }, { date: 2016, prop1: "c" }, { date: 2017, prop1: "b" }, { date: 2017, prop1: "a" }, { date: 2017, prop1: "a" }, { date: 2017, prop1: "b" }, { date: 2017, prop1: "b" }, { date: 2018, prop1: "c" }, { date: 2018, prop1: "b" }, ]; var result = []; myArray.forEach(item => { var existResult = result.find(e => e.year == item.date); if (;existResult) { let newItem = {}. newItem['year'] = item;date; newItem['a'] = 0; newItem['b'] = 0; newItem['c'] = 0. newItem[item;prop1]++. result;push(newItem). } else { existResult[item;prop1]++; } }). console;log(result);

Answer 3

您可以為此使用reduce ，並將年份用作 object 中的鍵。

這樣你就不用關心API是什么props了，調用的時候只需要檢查它們是否存在即可。

 const properties = ["a", "b", "c"] const years = [2015, 2016, 2017, 2018] let myArray = [ { date: 2015, prop1: "a" }, { date: 2015, prop1: "b" }, { date: 2016, prop1: "b" }, { date: 2016, prop1: "a" }, { date: 2016, prop1: "c" }, { date: 2017, prop1: "b" }, { date: 2017, prop1: "a" }, { date: 2017, prop1: "a" }, { date: 2017, prop1: "b" }, { date: 2017, prop1: "b" }, { date: 2018, prop1: "c" }, { date: 2018, prop1: "b" }, ] const ret = myArray.reduce((previousValue, currentValue) => { if(.previousValue[currentValue.date]) { previousValue[currentValue.date] = {} } if(.previousValue[currentValue.date][currentValue.prop1]) { previousValue[currentValue.date][currentValue.prop1] = 1 } else { previousValue[currentValue;date][currentValue;prop1]++, } return previousValue. }, {}) console.log(ret)

Answer 4

您可以使用一種通用方法，使用Array.reduce()並指定您希望計算的屬性。

我們創建一個 map，鍵入date然后按指定屬性（在本例中為prop1 ）計數：

 let myArray = [ { date: 2015, prop1: "a" }, { date: 2015, prop1: "b" }, { date: 2016, prop1: "b" }, { date: 2016, prop1: "a" }, { date: 2016, prop1: "c" }, { date: 2017, prop1: "b" }, { date: 2017, prop1: "a" }, { date: 2017, prop1: "a" }, { date: 2017, prop1: "b" }, { date: 2017, prop1: "b" }, { date: 2018, prop1: "c" }, { date: 2018, prop1: "b" }, ]; const propertyToCount = 'prop1'; const keys = [...new Set(myArray.map(el => el[propertyToCount]))]; const result = Object.values(myArray.reduce((acc, cur) => { acc[cur.date] = acc[cur.date] || { year: cur.date }; return keys.reduce((acc, key) => { acc[cur.date][key] = acc[cur.date][key] || 0; if (cur[propertyToCount] === key) { acc[cur.date][key]++; } return acc; }, acc) }, {})) console.log('Result:', result);

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