Applying reduce method for accessing object information within an array and transforming its structure

Question

Applying reduce method for accessing object information within an array and transforming its structure

In my data structure, I have a list of deliveries that includes different cities and the number of units delivered to each city:

var deliveries = [{
    location: "Chicago",
    units: 10
}, {
    location: "San Francisco",
    units: 5
}, {
    location: "Miami",
    units: 2
}, {
    location: "San Francisco",
    units: 13
}, {
    location: "San Francisco",
    units: 2
}, {
    location: "Chicago",
    units: 16
}, {
    location: "Miami",
    units: 1
}];

I want to be able to query any city in the list and retrieve the number of times it appears along with the total units delivered to that city. The code I currently use for this purpose is:

function getData(arr, city) {
    var numberOfdeliveries = 0;
    var totalUnitsDelivered = 0;

    arr.forEach(function(val, index, arr) {
        if (val.location === city) {
            numberOfdeliveries += 1;
            totalUnitsDelivered += val.units

        }
    })
    return "number of deliveries: " + numberOfdeliveries + ". Total units:" + totalUnitsDelivered
}

getData(deliveries, "San Francisco"); // number of deliveries: 3. Total units:20

This function works accurately.

However, I am interested in exploring if using reduce can provide an array containing all cities with their respective delivery counts and total units. The desired output should resemble:

[{
    "Chicago": 2,
    units: 26
}, {
    "San Francisco":20,
    units: 5
}, {
    "Miami": 2,
    units: 3
}];

Thus far, my attempts have resulted in an object displaying only the count of appearances of each city:

var deliveries = [{
    location: "Chicago",
    units: 10
}, {
    location: "San Francisco",
    units: 5
}, {
    location: "Miami",
    units: 2
}, {
    location: "San Francisco",
    units: 13
}, {
    location: "San Francisco",
    units: 2
}, {
    location: "Chicago",
    units: 16
}, {
    location: "Miami",
    units: 1
}];

var answer = deliveries.reduce(function(obj, val, index, all) {
    if (!obj[val.location]) {
        obj[val.location] = 1
    } else {
        obj[val.location]++
    }

    return obj

}, {})

console.log(answer);  //{ Chicago: 2, 'San Francisco': 3, Miami: 2 }

javascript reduce

Answer 1

Answer №1

To optimize this code, consider using a result array along with a hash table to keep track of references to elements in the result array.

let orders = [{ product: "Apple", quantity: 10 }, { product: "Banana", quantity: 5 }, { product: "Orange", quantity: 2 }, { product: "Banana", quantity: 13 }, { product: "Banana", quantity: 2 }, { product: "Apple", quantity: 16 }, { product: "Orange", quantity: 1 }],
    groups = orders.reduce(function (hash) {
        return function (result, item) {
            if (!hash[item.product]) {
                hash[item.product] = {};
                hash[item.product][item.product] = 0;
                hash[item.product].quantity = 0;
                result.push(hash[item.product]);
            }
            hash[item.product][item.product]++;
            hash[item.product].quantity += item.quantity;
            return result;
        };
    }(Object.create(null)), []);

console.log(groups);

Answer 2

To optimize this code, consider using a result array along with a hash table to keep track of references to elements in the result array.

let orders = [{ product: "Apple", quantity: 10 }, { product: "Banana", quantity: 5 }, { product: "Orange", quantity: 2 }, { product: "Banana", quantity: 13 }, { product: "Banana", quantity: 2 }, { product: "Apple", quantity: 16 }, { product: "Orange", quantity: 1 }],
    groups = orders.reduce(function (hash) {
        return function (result, item) {
            if (!hash[item.product]) {
                hash[item.product] = {};
                hash[item.product][item.product] = 0;
                hash[item.product].quantity = 0;
                result.push(hash[item.product]);
            }
            hash[item.product][item.product]++;
            hash[item.product].quantity += item.quantity;
            return result;
        };
    }(Object.create(null)), []);

console.log(groups);

Answer 3

Answer №2

If you're going to run this query multiple times, it would be more efficient to map your data to a hashmap object using cities as the keys

var cities ={};
deliveries.foreach(function(item){
   var cityObj = cities[item.location] ?  cities[item.location] :{units:0, count:0}

   cityObj.units += item.units;
   cityObj.count ++;

});

This will result in something like:

{ "New York" :{units: 8, count:3},
  "Los Angeles":{units: 6, count:2}
}

Then, when you require the values:

var city="New York",
    units = cities[city].units;

Answer 4

If you're going to run this query multiple times, it would be more efficient to map your data to a hashmap object using cities as the keys

var cities ={};
deliveries.foreach(function(item){
   var cityObj = cities[item.location] ?  cities[item.location] :{units:0, count:0}

   cityObj.units += item.units;
   cityObj.count ++;

});

This will result in something like:

{ "New York" :{units: 8, count:3},
  "Los Angeles":{units: 6, count:2}
}

Then, when you require the values:

var city="New York",
    units = cities[city].units;

Answer 5

Answer №3

Although Nina technically provided an answer, I found charlietfl's idea of using a hash map to be more effective (despite their code not working). Intrigued, I decided to implement my own hash map using the reduce method. While I ultimately awarded the answer to Nina for being "correct," here is the solution I crafted:

var deliveries = [{
    location: "Chicago",
    units: 10
}, {
    location: "San Francisco",
    units: 5
}, {
    location: "Miami",
    units: 2
}, {
    location: "San Francisco",
    units: 13
}, {
    location: "San Francisco",
    units: 2
}, {
    location: "Chicago",
    units: 16
}, {
    location: "Miami",
    units: 1
}];

var answer = deliveries.reduce(function(obj, val, index, all) {
    if (!obj[val.location]) {
        obj[val.location] = {
            times: 1,
            units: val.units
        }
    } else {

        obj[val.location].times += 1;
        obj[val.location].units += val.units;
    }

    return obj

}, {});

console.log(answer);

Answer 6

Although Nina technically provided an answer, I found charlietfl's idea of using a hash map to be more effective (despite their code not working). Intrigued, I decided to implement my own hash map using the reduce method. While I ultimately awarded the answer to Nina for being "correct," here is the solution I crafted:

var deliveries = [{
    location: "Chicago",
    units: 10
}, {
    location: "San Francisco",
    units: 5
}, {
    location: "Miami",
    units: 2
}, {
    location: "San Francisco",
    units: 13
}, {
    location: "San Francisco",
    units: 2
}, {
    location: "Chicago",
    units: 16
}, {
    location: "Miami",
    units: 1
}];

var answer = deliveries.reduce(function(obj, val, index, all) {
    if (!obj[val.location]) {
        obj[val.location] = {
            times: 1,
            units: val.units
        }
    } else {

        obj[val.location].times += 1;
        obj[val.location].units += val.units;
    }

    return obj

}, {});

console.log(answer);

Answer 7

Answer №4

To achieve grouping, utilize Map objects.

var shipments = [{ location: "New York", units: 8 }, { location: "Los Angeles", units: 3 }, { location: "Dallas", units: 6 }, { location: "Los Angeles", units: 10 }, { location: "Chicago", units: 4 }, { location: "Dallas", units: 9 }];

var groupedResults = [];
shipments.reduce(
(locations, shipment) => locations.set(shipment.location, [...(locations.get(shipment.location) || []), shipment]), new Map
).forEach((shipments, city) => {
var summary = {};
summary[city] = shipments.length;
summary.units = shipments.reduce((totalUnits, currentShipment) => totalUnits + currentShipment.units, 0);
groupedResults.push(summary);
})
console.log(groupedResults);

Answer 8

To achieve grouping, utilize Map objects.

var shipments = [{ location: "New York", units: 8 }, { location: "Los Angeles", units: 3 }, { location: "Dallas", units: 6 }, { location: "Los Angeles", units: 10 }, { location: "Chicago", units: 4 }, { location: "Dallas", units: 9 }];

var groupedResults = [];
shipments.reduce(
(locations, shipment) => locations.set(shipment.location, [...(locations.get(shipment.location) || []), shipment]), new Map
).forEach((shipments, city) => {
var summary = {};
summary[city] = shipments.length;
summary.units = shipments.reduce((totalUnits, currentShipment) => totalUnits + currentShipment.units, 0);
groupedResults.push(summary);
})
console.log(groupedResults);

Applying reduce method for accessing object information within an array and transforming its structure

Answer №1

Answer №2

Answer №3

Answer №4

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