Javascript - Counting duplicates in object array and storing the count as a new object
I have an array of javascript objects that are products. These products are displayed in a list as a cart.
I want to count the number of duplicate products in the array based in the _.id value and remove these objects from the array and relace them with an updated version and a new key called count with a value of the total number of times this object comes up.
So far, I have tried numerous methods and I've searched all over google but there's nothing that I've found that can do the job correctly.
An example of the type of array that I will be using would be this:
[
{ _id: "5971df93bfef201237985c4d",
slug: "5971df93bfef201237985c4d",
taxPercentage: 23,
totalCost: 9.99,
currency: "EUR",
},
]
so what I would want my end result to be would be something like this - it removes the duplicate value and replaces it with the same object but adds a new key called count with a value of the number of times the object initially was in the array:
[
{ _id: "5971df93bfef201237985c4d",
slug: "5971df93bfef201237985c4d",
taxPercentage: 23,
totalCost: 9.99,
currency: "EUR",
count: 2, // whatever the count is
},
]
So far I'm using this method:
var count = [];
if (cart.cart.products != undefined) {
let namestUi = {
renderNames(names){
return Array.from(
names.reduce( (counters, object) =>
counters.set(object._id, (counters.get(object._id) || 0) + 1),
new Map() ),
([object, count]) => {
var filterObj = names.filter(function(e) {
return e._id == object;
});
return ({filterObj, count})
}
);
}
};
count = namestUi.renderNames(cart.cart.products);
console.log(count)
}
but it returns the values like this:
{filterObj: Array // the array of the duplicates, count: 2}
{filterObj: Array, count: 1}
and since I am using React-Native with a list view something like this won't work.
It just needs to store the items the way it was before (an array) but with a new child called count.
Any help is welcomed!
Answers:
I would stick to reduce, use a Map and spread its values to get the final result:
const names = [{ _id: 1 }, { _id: 1}, { _id: 2}, { _id: 1}];
const result = [...names.reduce( (mp, o) => {
if (!mp.has(o._id)) mp.set(o._id, { ...o, count: 0 });
mp.get(o._id).count++;
return mp;
}, new Map).values()];
console.log(result);When you would have more than one key, then one idea is to join those with JSON.stringify([ ]):
const names = [{cat: 1, sub: 1}, {cat: 1, sub: 2}, {cat: 2, sub: 1}, {cat: 1, sub: 1}];
const result = [...names.reduce( (mp, o) => {
const key = JSON.stringify([o.cat, o.sub]);
if (!mp.has(key)) mp.set(key, { ...o, count: 0 });
mp.get(key).count++;
return mp;
}, new Map).values()];
console.log(result);The easiest would be probably a map:
var map=new Map();
names.forEach(function(el){
if(map.has(el["_id"])){
map.get(el["_id"]).count++;
}else{
map.set(el["_id"],Object.assign(el,{count:1}));
}
});
And then recreate an array:
names=[...map.values()];
Or in old hash/array way:
var hash={},result=[];
names.forEach(function(name){
var id=name["_id"];
if(hash[id]){
hash[id].count++;
}else{
result.push(hash[id]={
count:1,
...name
});
}
});
console.log(result);
You can make use of array.reduce method to convert an original array into a new array with desired structure.
We can just check if the id exists in the array and accordingly update the array with new object having count property.
let arr = [{
id: 1
}, {
id: 1
}, {
id: 1
}, {
id: 2
}, {
id: 2
}];
let new_arr = arr.reduce((ar, obj) => {
let bool = false;
if (!ar) {
ar = [];
}
ar.forEach((a) => {
if (a.id === obj.id) {
a.count++;
bool = true;
}
});
if (!bool) {
obj.count = 1;
ar.push(obj);
}
return ar;
}, []);
console.log(new_arr);