如何對 JavaScript 中具有相同值的數組求和？

Question

這是我的數組，我從 Firebase 和一個監聽器拉出來。

[{"Amount": "40", "Day": "08/31/2022"}, {"Amount": "300", "Day": "09/01/2022"}, {"Amount": "1715", "Day": "08/31/2022"}, {"Amount": "250", "Day": "08/31/2022"}, {"Amount": "100", "Day": "08/31/2022"}, {"Amount": "200", "Day": "08/31/2022"}]

我希望這個數組在同一天總結所有值，並只返回一個總和。 所以我可以將它用於 React Native 中帶有勝利原生的圖表。

這是我的代碼，它運行良好，但我一直在互聯網上尋找如何總結，但到目前為止還沒有運氣！

  const q = query(collection(db, "users"), where("moneda", "==", "$"));
  const unsubscribe = onSnapshot(q,(querySnapshot) => {
    const dolarCurrency = [];
    const months =[];
    querySnapshot.forEach((doc) =>{
      dolarCurrency.push(doc.data().cantidad);
      months.push(doc.data().fecha)
    })
    const hash = months.map((Day) => ({ Day }));
    const hashDolar = dolarCurrency.map(( Amount ) => ({ Amount }))

    const output = hash.map(({Day},i) => ({Day, ...hashDolar[i]}));

    console.log(output)
  })

任何幫助或建議將不勝感激我的朋友！

Answer 1

減少數組 function 可以解決您的問題。

const output = [{"Amount": "40", "Day": "08/31/2022"}, {"Amount": "300", "Day": "09/01/2022"}, {"Amount": "1715", "Day": "08/31/2022"}, {"Amount": "250", "Day": "08/31/2022"}, {"Amount": "100", "Day": "08/31/2022"}, {"Amount": "200", "Day": "08/31/2022"}]

const sum = output.reduce((acc, cur)=> {
    const found = acc.find(val => val.Day === cur.Day)
    if(found){
        found.Amount+=Number(cur.Amount)
    }
    else{
        acc.push({...cur, Amount: Number(cur.Amount)})
    }
    return acc
}, [])

console.log(sum)

Answer 2

1. 創建一個新的 object 可以存儲鍵/值對，其中鍵是日期。
2. 如果日期不存在，則迭代對象添加日期作為鍵，並將其初始化為 object，日期和數量設置為零。
3. 將該日期的當前金額值添加到 object 中的金額存儲中。
4. 最后，循環完成后，使用Object.values將這些對象放入一個新數組中。

 const arr = [{"Amount": "40", "Day": "08/31/2022"}, {"Amount": "300", "Day": "09/01/2022"}, {"Amount": "1715", "Day": "08/31/2022"}, {"Amount": "250", "Day": "08/31/2022"}, {"Amount": "100", "Day": "08/31/2022"}, {"Amount": "200", "Day": "08/31/2022"}]; const out = {}; for (const { Amount, Day } of arr) { out[Day]??= { Day, Amount: 0 }; const subtotal = out[Day].Amount + Number(Amount); out[Day] = {...out[Day], Amount: subtotal }; } console.log(Object.values(out));