有沒有辦法有效地“旋轉”多維陣列？

我有一個按以下方式格式化的陣列陣列：

[['BTC', '2022-04-27', '39151.53'],
 ['BTC', '2022-04-26', '37730.20'],
 ['BTC', '2022-04-25', '39151.53'],
 ['ETH', '2022-04-27', '39151.53'],
 ['ETH', '2022-04-26', '37730.20'],
 ['ETH', '2022-04-25', '39151.53']]

我想結束的是：

[['Date', 'BTC, 'ETH'],
 ['2022-04-27', '39151.53', '39151.53'],
 ['2022-04-26', '37730.20', '39151.53'],
 ['2022-04-25', '39151.53', '39151.53']]

有沒有簡單的方法來解決它？

uj5u.com熱心網友回復：

這里使用另一個解決方案reduce()。

這首先創建一個 JavaScript 物件，該物件將允許在程式中快速查找給定貨幣和日期的特定值，然后轉換該物件以創建 OP 請求的結果。例如，當給定貨幣和日期有兩個值時，它也會因輸入資料不正確而引發錯誤。

const input = [
  ["BTC", "2022-04-27", "39151.53"],
  ["BTC", "2022-04-26", "37730.20"],
  ["BTC", "2022-04-25", "39151.53"],
  ["ETH", "2022-04-27", "39151.53"],
  ["ETH", "2022-04-26", "37730.20"],
  ["ETH", "2022-04-25", "39151.53"],
];

function pivot(input){
  return input.reduce((perDay, [currency, date, value]) => {
    if(perDay[date]) {
      // we already have a value for this day
      if(perDay[date][currency]){
        // we already have a value for this currency and day => error
        throw new Error(`Two values for for the same day. Currency: ${currency}, Day: ${date}`);
      }
      // add value for another currency for that day
      else perDay[date][currency] = value;
    } else perDay[date] = { [currency]: value };
    return perDay; 
  }, {})
}

// result as a JS object which will allow quick lookups
const pivotted = pivot(input);
console.log("Result as JavaScript object")
console.log(pivotted);

// result transformed to your expected result
const result = Object.entries(pivotted).map(([date, values]) => [date, ...Object.values(values)]);
result.unshift(['Date', 'BTC', 'ETH']);
console.log("Result as JavaScript nested array")
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

uj5u.com熱心網友回復：

看起來 OP 需要由日期欄位索引的內部陣列。這可以通過減少來完成。一旦有了索引，遍歷鍵（日期）并收集與每個日期關聯的值。

const array = [['BTC', '2022-04-27', '39151.53'],
 ['BTC', '2022-04-26', '37730.20'],
 ['BTC', '2022-04-25', '39151.53'],
 ['ETH', '2022-04-27', '39151.53'],
 ['ETH', '2022-04-26', '37730.20'],
 ['ETH', '2022-04-25', '39151.53']];

const dateIndex = array.reduce((acc, a) => {
  let date = a[1];
  if (!acc[date]) acc[date] = [];
  acc[date].push(a);
  return acc;
}, {});


let result = [['Date', 'BTC', 'ETH']];
Object.keys(dateIndex).map(date => {
  let values = dateIndex[date].map(arr => arr[2]);
  result.push([date, ...values]);
});

console.log(result)

uj5u.com熱心網友回復：

您可以使用具有列型別和目標索引的物件。然后找到該行并將型別分配給所需的單元格。

const
    data = [['BTC', '2022-04-27', '39151.53'], ['BTC', '2022-04-26', '37730.20'], ['BTC', '2022-04-25', '39151.53'], ['ETH', '2022-04-27', '39151.53'], ['ETH', '2022-04-26', '37730.20'], ['ETH', '2022-04-25', '39151.53']],
    types = { Date: 0, BTC: 1, ETH: 2 },
    result = data.reduce((r, [type, date, value]) => {
        let row = r.find(a => a[types.Date] === date);
        if (!row) r.push(row = [date, ...Array(Object.keys(types).length - 1).fill('0')]);
        row[types[type]] = value;
        return r;
    }, [Object.keys(types)]);

console.log(result);

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