How to count all unique values in an array of objects?

Question

I want to create an array with a uniqueDate value in my array. So if I have this array:

const arr = [
      {
        name: "Edward",
        date: "24 March"
      },
      {
        name: "Banana",
        date: "12 March"
      },
      {
        name: "Edward",
        date: "23 March"
      },
      {
        name: "Edward",
        date: "23 March"
      }
    ]

... then the output will be something like:

[
    {name:"Edward", uniqueDate: 2, totalSubmit: 3},   
    {nama: "Banana",uniqueDate: 1, totalSubmit: 1}
]

The first unique date is 2 because we have 2 different dates: 24 March and 23 March. I've tried to use reduce, but it has some issues.

Example I have this array: const arr = [ { nama: "Edward", date: "24 March" }, { nama: "Banana", date: "12 March" }, { nama: "Edward", date: "23 March" }, { nama: "Edward", date: "23 March" }, { nama: "Bob", date: "1 March" }, { nama: "Pam", date: "1 March" }, { nama: "Anna", date: "19 March" }, { nama: "Jake", date: "12 March" } ] — Edward Tanoto
– Edward Tanoto, Commented Mar 27, 2021 at 20:24
I reduced it twice, const reducedSales = arr.reduce((acc, item) => { var previousItem = acc.find(findItem => (findItem['nama'] === item['nama']) && (findItem['date'] === item['date'])); // if previous item is false, meaning different Nama Distributor if (!previousItem) { acc.push({ ...item, totalSubmit: 1 }) } else { previousItem.totalSubmit++ } return acc; }, []) — Edward Tanoto
– Edward Tanoto, Commented Mar 27, 2021 at 20:25
and another reduce, const update = reducedSales.reduce((acc, item) => { var previousItem = acc.find(findItem => findItem['nama'] === item['nama']); // if previous item is false, meaning different Nama Distributor if (!previousItem) { acc.push({ ...item, hariKerja: 1 }) } else { previousItem.hariKerja++ } return acc; }, []) console.log(update) — Edward Tanoto
– Edward Tanoto, Commented Mar 27, 2021 at 20:25
@AndrewL64 this is the output: [ { nama: 'Edward', date: '24 March', totalSubmit: 1, hariKerja: 2 }, { nama: 'Banana', date: '12 March', totalSubmit: 1, hariKerja: 1 }, { nama: 'Bob', date: '1 March', totalSubmit: 1, hariKerja: 1 }, { nama: 'Pam', date: '1 March', totalSubmit: 1, hariKerja: 1 }, { nama: 'Anna', date: '19 March', totalSubmit: 1, hariKerja: 1 }, { nama: 'Jake', date: '12 March', totalSubmit: 1, hariKerja: 1 } ] — Edward Tanoto
– Edward Tanoto, Commented Mar 27, 2021 at 20:25

trincot · Accepted Answer · 2021-03-27 22:33:14Z

3

You can use a Map to collect the dates that go with a name (check your spelling in the example data!), and then you can iterate those map entries to both get the dates-array length, and unique count (via Set):

const arr = [{name: "Edward",date: "24 March"},{name: "Banana",date: "12 March"},{name: "Edward",date: "23 March"},{name: "Edward",date: "23 March"}];

let map = new Map(arr.map(o => [o.name, []]));
for (let {name, date} of arr) map.get(name).push(date);
let result = Array.from(map.entries(), ([name, dates]) => 
    ({name, uniqueDate: new Set(dates).size, totalSubmit: dates.length})
);
console.log(result);

If the property name to group by has special characters, like a space, then:

const arr = [{"Full Name": "Edward",date: "24 March"},{"Full Name": "Banana",date: "12 March"},{"Full Name": "Edward",date: "23 March"},{"Full Name": "Edward",date: "23 March"}];

let map = new Map(arr.map(o => [o["Full Name"], []]));
for (let o of arr) map.get(o["Full Name"]).push(o.date);
let result = Array.from(map.entries(), ([name, dates]) => 
    ({"Full Name": name, uniqueDate: new Set(dates).size, totalSubmit: dates.length})
);
console.log(result);

edited Mar 27, 2021 at 22:33

answered Mar 27, 2021 at 20:31

trincot

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4 Comments

Edward Tanoto Over a year ago

Hi, thank you very much for your help. If I may add 1 more question, what if my object name has a space? For example, instead of name, the object name is Full Name. Instead of date, the object name is 'Created At'.

Edward Tanoto Over a year ago

for (let {name, date} of arr) map.get(name).push(date); TypeError: Cannot read property 'push' of undefined So for context, my object name is something like "Full Name", and "Created At".

Edward Tanoto Over a year ago

So the actual array is something like: const arr = [{"Full Name": "Edward","Created At": "24 March"}]; etc

trincot Over a year ago

See addition to answer.

fyasir · Accepted Answer · 2021-03-27 20:58:23Z

1

You can call reduce function to create a key-value pair of each name then, where it contains the name, a Set of unique dates, and totalSubmit. Finally, you can get the values of that object and map it with the unique dates' size.

const arr = [{ name: "Edward", date: "24 March" }, { name: "Banana", date: "12 March" }, { name: "Edward", date: "23 March" }, { name: "Edward", date: "23 March" }];
    
const temp = arr.reduce((acc, { name, date }) => {
   acc[name] = acc[name] || { name, dates: new Set(), totalSubmit: 0 };
   acc[name].totalSubmit++;
   acc[name].dates.add(date);
   return acc;
}, {});
    
const result = Object.values(temp).map(({ name, dates, totalSubmit}) => ({ name, uniqueDate: dates.size, totalSubmit }));
     
console.log(result);

edited Mar 27, 2021 at 20:58

answered Mar 27, 2021 at 20:49

fyasir

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2 Comments

Edward Tanoto Over a year ago

Thank you so much for your answer! May I add 1 more question? What if my object name has space? Example: instead of "name", its "Full Name"

fyasir Over a year ago

@EdwardTanoto I assume this "Full Name" would be unique. in this case, we can use key = name.split(' ').join('_') which makes Edward Tanoto into Edward_Tanoto

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