Javascript - count each interaction of a reduce

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August 14, 2023
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2 Answers

I have a list of objects like

const usageCosts = {
    224910186407: {
        deviceId: "224910186407",
        currency: "GBP",
        yearlyUsage: 1480.81
    },
    224910464538: {
        deviceId: "224910464538",
        currency: "GBP",
        yearlyUsage: 617.36
    },
    224910464577: {
        deviceId: "224910464577",
        currency: "EUR",
        yearlyUsage: 522.3
    }
}

I’m reducing it to sum by currency like

 const totalYearlyCost = Object.values(usageCosts).reduce(
      (acc: { [key: string]: any }, stat: any) => {
        if (stat.currency && !acc[stat.currency]) {
          acc[stat.currency] = 0
        }
        return {
          ...acc,
          [stat.currency!]: acc[stat.currency!] + stat.yearlyUsage,
        }
      },
      {},
    )

and it returns an object like

{
EUR: 522.3
GBP: 2,098.17
}

I want to also return the total devices of each currency, something like:

{
EUR: 522.3 (1 device)
GBP: 2,098.17 (2 devices)
}

tried to add another loop but it’s not working as expected

Answers

It’s a lot easier to do this in 2 parts.

First reduce it to an array with the grouped values.

Then loop over (could also a reduce ofc) the object, and get the sum of the array, and add ${array.length} devices to the string:

const usageCosts = {
    224910186407: {
        deviceId: "224910186407",
        currency: "GBP",
        yearlyUsage: 1480.81
    },
    224910464538: {
        deviceId: "224910464538",
        currency: "GBP",
        yearlyUsage: 617.36
    },
    224910464577: {
        deviceId: "224910464577",
        currency: "EUR",
        yearlyUsage: 522.3
    }
}

let grouped = Object.values(usageCosts).reduce((p, c) => {
    if (!p[c.currency]) p[c.currency] = [];
    p[c.currency].push(c.yearlyUsage);
    return p;
}, {});

for (var key in grouped) {
    grouped[key] = `${grouped[key].reduce((a,b)=>a+b)} (${grouped[key].length}) devices`;
}

console.log(grouped)

here is a solution:

const result = Object.values(usageCosts).reduce((acc, stat) => {
    if (stat.currency && !acc[stat.currency]) {
        acc[stat.currency] = {
            total: 0,
            devices: 0,
        }
    }

    return {
        ...acc,
        [stat.currency]: {
            total: acc[stat.currency].total + stat.yearlyUsage,
            devices: acc[stat.currency].devices + 1,
        }
    };
}, {});

As a result, you will get the following structure:

{
  GBP: { total: 2098.17, devices: 2 },
  EUR: { total: 522.3, devices: 1 }
}

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Javascript – count each interaction of a reduce

Answers