Is there a way to efficiently "pivot" a multidimensional array?-CodePudding

I have an array of arrays formatted the following way:

[['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']]

What I would like to end up with is:

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

Is there any non-complicated way to solve it?

CodePudding user response：

Here another solution using reduce().

This first creates a JavaScript object which would allow for quick lookups of a specific value for a given currency and date within a program and then transforms that object to create the result requested by OP. It will also throw an error for incorrect input data when e.g. there would be two values for a given currency and date.

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);

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CodePudding user response：

It looks like the OP needs the inner arrays indexed by the date field. This can be done with reduce. Once there's an index, walk through the keys (dates) and collect the values associated with each date.

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)

CodePudding user response：

You could take an object with the types fo the columns and the indices of the target. Then find the row and assign the type to the wanted cell.

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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