<p>I have a list of objects as follows: </p> <pre class="brush:php;toolbar:false;">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 } }</pre> <p>I'm doing a sum by currency, like this: </p> <pre class="brush:php;toolbar:false;">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, } }, {}, )</pre> <p>It returns an object as follows: </p> <pre class="brush:php;toolbar:false;">{ EUR: 522.3 GBP: 2,098.17 }</pre> <p>I also want to return the total number of devices per currency, something like: </p> <pre class="brush:php;toolbar:false;">{ EUR: 522.3 (1 device) GBP: 2,098.17 (2 devices) }</pre> <p>Tried adding another loop, but the results were not as expected. </p>

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)