sort an array of objects based on previous and next id

Question

I have an array of task objects containing previous and next task ids. I need to display an array of tasks which are sorted based on previous and next task ids. For example:

My input task array is

 [
    {
    "taskId": "101",
    "previousTaskId":"0",
    "nextTaskId":"102"
    },

    {
    "taskId": "103",
    "previousTaskId":"102",
    "nextTaskId":"0"
    },

    {
    "taskId": "102",
    "previousTaskId":"101",
    "nextTaskId":"103"
    }
]

My output task array is:

[
    {
    "taskId": "101",
    "previousTaskId":"0",
    "nextTaskId":"102"
    },

    {
    "taskId": "102",
    "previousTaskId":"101",
    "nextTaskId":"103"
    },

    {
    "taskId": "103",
    "previousTaskId":"102",
    "nextTaskId":"0"
    }
]

Is there any way to implement it using es6 methods? I am trying to use reduce and map functionality

const sortedTasks = tasks.reduce((acc, task) => {
    let {taskId, previousTaskId, nextTaskId} = task;
    return {...acc, task.map(function(item){
        if(item.previousTaskId === 0) //first position
            //how to compare with another taskId and assign it to acc ?

         })
    };
}, {});

what baout zero as id? do you have always zero at start and end? — Nina Scholz
– Nina Scholz, Commented May 31, 2021 at 10:18
The input array is coming from an ajax call and yes the first object.previousTaskId is always 0 and endObject.nextTaskId is 0 — user596502
– user596502, Commented May 31, 2021 at 10:27

Nina Scholz · Accepted Answer · 2021-05-31 10:46:22Z

2

You could build a reference from each predecessor to the node and build the result from zero.

function sort(array) {
    const
        temp = data.reduce((t, o) => {
            t[o.previousTaskId] = o;
            return t;
        }, {}),
        result = [];
    
    let p = '0';
    while (temp[p]) {
        result.push(temp[p]);
        p = temp[p]?.taskId;
    }
    return result;
}

const
    data = [{ taskId: "101", previousTaskId: "0", nextTaskId: "102" }, { taskId: "103", previousTaskId: "102", nextTaskId: "0" }, { taskId: "102", previousTaskId: "101", nextTaskId: "103" }];

console.log(sort(data));

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

answered May 31, 2021 at 10:46

Nina Scholz

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3 Comments

user596502 Over a year ago

Thanks a lot . Just to understand the code, I usually use ternary operator with ? followed by : I am slightly confused, What does this line mean p = temp[p]?.taskId;

Nina Scholz Over a year ago

it is the optional chaining operator ?..

user596502 Over a year ago

I see. If a reference is null or undefined, the expression short-circuits with a return value of undefined, instead of causing an error. Thanks

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