How to allocate data proportionally

Question

I have an array

let arr = [
    { type: 1, title: 1 },
    { type: 1, title: 1 },
    { type: 2, title: 1 },
    { type: 2, title: 1 },
    { type: 2, title: 1 },
    { type: 2, title: 1 },
    { type: 2, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 1, title: 1 },
    { type: 1, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 1, title: 1 },
    { type: 1, title: 1 },
    { type: 3, title: 1 },
    { type: 3, title: 1 },
    { type: 1, title: 1 },
    { type: 1, title: 1 }]

I want data = 1（type==1）：2(type==2)：1type==1(3) （5:10:5）

There may be a lot of data, but no matter how much data there is, I only hope to finally get 1:2:1 data I want last result, for example

last arr =  [
    {
        type: 1,
        child: [{ type: 1, title: 1 },{ type: 1, title: 1 },{ type: 1, title: 1 },{ type: 1, title: 1 },{ type: 1, title: 1 }]
    },
    {
        type: 2,
        child: [{ type: 2, title: 1 },{ type: 2, title: 1 },{ type: 2, title: 1 },{ type: 2, title: 1 },{ type: 2, title: 1 },{ type: 2, title: 1 },{ type: 2, title: 1 },{ type: 2, title: 1 },{ type: 2, title: 1 },{ type: 2, title: 1 }]
    },
    {
        type: 3,
        child: [{ type: 3, title: 1 },{ type: 3, title: 1 },{ type: 3, title: 1 },{ type: 3, title: 1 },{ type: 3, title: 1 }]
    }
]

Does this answer your question? [How to group an array of objects by key](https://stackoverflow.com/questions/40774697/how-to-group-an-array-of-objects-by-key) — Jelle, Nov 22 '21 at 08:01

Terry Lennox · Accepted Answer · 2021-11-22T11:39:25.233

To get the desired output, in the desired ratio, we can loop, adding the correct ratio of items to the output, from the input array, until no more addition is possible, or we've reached the max count (in this case 20).

For example, if the ratio is 1:2:1, we add 1,2,1 items of each type for each iteration, stopping if

a.) There are no items of a given type left.
b.) We've reached our target count (in this case 20)

We create a function takeNItems() which removes N items of a certain type from an array and returns in another array.

        
let arr = [ { type: 1, title: 1 }, { type: 1, title: 1 }, { type: 2, title: 1 }, { type: 2, title: 1 }, { type: 2, title: 1 }, { type: 2, title: 1 }, { type: 2, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 1, title: 1 }, { type: 1, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 1, title: 1 }, { type: 1, title: 1 }, { type: 3, title: 1 }, { type: 3, title: 1 }, { type: 1, title: 1 }, { type: 1, title: 1 }, { type: 2, title: 1 }, { type: 2, title: 1 }, { type: 2, title: 1 }, { type: 2, title: 1 }, { type: 2, title: 1 }, ] 

// The ratios by type
const ratios = { 1: 1, 2: 2, 3: 1 };
const totalCount = 20;

function takeNItems(arr, type, count) {
    let result = [];
    do {
        let index = arr.findIndex(item => item.type === type);
        if (index === -1) return null; 
        result.push(...arr.splice(index, 1))   
    } while (result.length < count)
    return result;
}

let count = 0;
let roundCount = Object.values(ratios).reduce((sum, n) => sum + n,0);
let result = Object.keys(ratios).map(type => ({ type: +type, count: 0, child: [] }));

do { 
    let nextRound = result.map(({type}, i) => takeNItems(arr, type, ratios[type]));
    // Not enough items for another round...
    if (nextRound.flat().length < roundCount) break;
    nextRound.forEach((items, i) => { 
        result[i].count += items.length;
        result[i].child.push(...items);
    });
    count += nextRound.flat().length;
} while (count < totalCount);

console.log('Result:', result)

.as-console-wrapper { max-height: 100% !important; top: 0; }

I hope there are 20 pieces of final data and the data distribution is 1:2:1 — 李大白白, Nov 22 '21 at 08:17
It doesn't look like it from the example data you've given, however your real data may be different! — Terry Lennox, Nov 22 '21 at 08:18
I mean, no matter how much data there is, I only need to get 20 pieces of data in the ratio of 1:2:1 — 李大白白, Nov 22 '21 at 08:20
Thank you. It seems that I still need to learn more. You're very good — 李大白白, Nov 23 '21 at 00:50

How to allocate data proportionally

1 Answers1