Question 318615 in Javascript Question posted in
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Javascript – Sort Object Array by dependant property

I have an unsorted objects array with strings like this:

const unsortedArr =  [
  {
  id: "test13",
  startAfter: "test15"
  },
  {
  id: "test20",
  startAfter: "test5"
  },
  { 
  id: "test5",
  startAfter: "test1"
  },
  {
  id: "test15",
  startAfter: "test20"
  },
]

You get the idea.

I also have a start ID: const startId = "test1";

With my start ID as the first value, I want to sort the array according to the "startAfter" property. Create a chronological chain, so to speak.

The result should look like this:

const sortedArr =  [
    {
    id: "test5",
    startAfter: "test1"
    },
    {
    id: "test20",
    startAfter: "test5"
    },
    {
    id: "test15",
    startAfter: "test20"
    },
    {
    id: "test13",
    startAfter: "test15"
    },
    ]

What is the easiest way to sort this array in JS?

Tags:

2

Answers


  1. 0

    What you have is a linked list, but it lacks the possibility to locate an object by id in constant time. So I’d suggest creating a Map for that first, and then you can create the sorted array by looking up the next id from the current node:

    function sort(unsortedArr, startId) {
    const map = new Map(unsortedArr.map(o => [o.startAfter, o]));
    const sorted = [];
    for (let node = map.get(startId); node; node = map.get(node.id)) {
        sorted.push(node);
    }
    return sorted;
}

// Example run
const unsortedArr = [{id: "test13",startAfter: "test15"},{id: "test20",startAfter: "test5"},{ id: "test5",startAfter: "test1"},{id: "test15",startAfter: "test20"},];
const startId = "test1";
const sorted = sort(unsortedArr, startId);
console.log(sorted);
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  2. 0

    You can achieve this by creating a map of the array and then iterating over the map starting from the startId

    const sortArray = (unsortedArr, startId) => {
    // Create a map for quick lookup
    const map = new Map(unsortedArr.map(i => [i.id, i]));

    // The sorted array
    let sortedArr = [];
    let currentId = startId;

    while(map.has(currentId)) {
        // Get the item from the map
        const { id, startAfter } = map.get(currentId);

        // Add the item to the sorted array
        sortedArr = [...sortedArr, { id, startAfter }];

        currentId = startAfter;
    }

    return sortedArr;
}

// Usage
const unsortedArr = [
    { id: "test13", startAfter: "test15" },
    { id: "test20", startAfter: "test5" },
    { id: "test5", startAfter: "test1" },
    { id: "test15", startAfter: "test20" },
];

const startId = "test1";

const sortedArr = sortArray(unsortedArr, startId);

console.log(sortedArr);
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