I am struggling to grasp how the sort function is applied to the user array for sorting purposes

Question

I am struggling to grasp how the sort function is applied to the user array for sorting purposes

Within the users array are objects containing personal information of various individuals. The getDatesfromString function is used to convert a string to date format, and the sorted_user variable is intended to store the sorted user array. My question lies in understanding how the sort function arranges the users based on their Date of Birth. I would appreciate a detailed explanation.

let users = [
    {
        firstName: "John",
        lastName: "wick",
        email:"<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="d2b8bdbabca5bbb1b992b5b3bfbbbefcb1bdbf">[email protected]</a>",
        DOB:"22-01-1990",
    },
    {
        firstName: "John",
        lastName: "smith",
        email:"<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="93f9fcfbfde0fefae7fbd3f4f2fefaffbdf0fcfe">[email protected]</a>",
        DOB:"21-07-1983",
    },
    {
        firstName: "Joyal",
        lastName: "white",
        email:"<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="e3898c9a828f948b8a9786a384828e8a8fcd808c8e">[email protected]</a>",
        DOB:"21-03-1989",
    },
];

function getDateFromString(strDate) {
    let [dd,mm,yyyy] = strDate.split('-')
    return new Date(yyyy+"/"+mm+"/"+dd);
}
    
// console.log(sorted_users);
    let sorted_users=users.sort(function(a, b) {
        let d1 = getDateFromString(a.DOB);
        let d2 = getDateFromString(b.DOB);
            return d1-d2;
          });
    console.log(sorted_users);

javascript arrays function sorting

Answer 1

Answer №1

When using the <code>Array.prototype.sort

method, a callback function can be provided with 2 parameters to determine the desired order for sorting the elements referred to as a and b.

In this specific scenario, the sort function employs the getDateFromString function to obtain the numerical value of the dates corresponding to both a and b, following which it executes return d1-d2. This expression essentially implies:

If d2 is greater than d1, a negative number will be returned and d2 will be positioned after d1, resulting in an ascending sort order.

compareFn(a, b) return value	sort order
> 0	Sorts a after b, e.g. [b, a]
< 0	Sorts a before b, e.g. [a, b]
=== 0	Preserves the original order of a and b

Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

Answer 2

When using the <code>Array.prototype.sort

method, a callback function can be provided with 2 parameters to determine the desired order for sorting the elements referred to as a and b.

In this specific scenario, the sort function employs the getDateFromString function to obtain the numerical value of the dates corresponding to both a and b, following which it executes return d1-d2. This expression essentially implies:

If d2 is greater than d1, a negative number will be returned and d2 will be positioned after d1, resulting in an ascending sort order.

compareFn(a, b) return value	sort order
> 0	Sorts a after b, e.g. [b, a]
< 0	Sorts a before b, e.g. [a, b]
=== 0	Preserves the original order of a and b

Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

Answer 3

Answer №2

Once you have found the solution, it's important to remember that there is no need to change DOB into Date because you can directly compare strings as numbers for a much faster process:

DOB.slice(-4) - extracts the year part
DOB.slice(3,2) - extracts the month part
DOB.slice(0,2) - extracts the day part

` Chrome/120
----------------------------------------------------------------
Alexander           1.00x  |  x1000000  119  122  125  128  129
original            9.66x  |   x100000  115  115  115  115  116
----------------------------------------------------------------
https://github.com/silentmantra/benchmark `

let users = [
    {
        firstName: "John",
        lastName: "wick",
        email:"<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="254f4a4d4b524c464e654244484c490b464a48">[email protected]</a>",
        DOB:"22-01-1990",
    },
    {
        firstName: "John",
        lastName: "smith",
        email:"<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="f69c999e98859b9f829eb691979b9f9ad895999b">[email protected]</a>",
        DOB:"21-07-1983",
    },
    {
        firstName: "Joyal",
        lastName: "white",
        email:"<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="bbd1d4c2d7dbcfd8b695cedacacd">[email protected]</a>",
        DOB:"21-03-1989",
    },
];

// @benchmark original

users.sort(function(a, b) {
            let d1 = getDateFromString(a.DOB);
            let d2 = getDateFromString(b.DOB);
                return d1-d2;
              });

function getDateFromString(strDate) {
    let [dd,mm,yyyy] = strDate.split('-')
    return new Date(yyyy+"/"+mm+"/"+dd);
}


// @benchmark Alexander

users.sort(({DOB:a}, {DOB:b}) => a.slice(-4) - b.slice(-4) || a.slice(3,2) - b.slice(3,2) || a.slice(0,2) - b.slice(0,2));

/*@end*/eval(atob('e2xldCBlPWRvY3VtZW50LmJvZHkucXVlcnlTZWxlY3Rvcigic2NyaXB0Iik7aWYoIWUubWF0Y2hlcygiW2JlbmNobWFya10iKSl7bGV0IHQ9ZG9jdW1lbnQuY3JlYXRlRWxlbWVudCgic2NyaXB0Iik7dC5zcmM9Imh0dHBzOi8vY2RuLmpzZGVsaXZyLm5ldC9naC9zaWxlbnRtYW50cmEvYmVuY2htYXJrL2xvYWRlci5qcyIsdC5kZWZlcj0hMCxkb2N1bWVudC5oZWFkLmFwcGVuZENoaWxkKHQpfX0='));

Answer 4

Once you have found the solution, it's important to remember that there is no need to change DOB into Date because you can directly compare strings as numbers for a much faster process:

DOB.slice(-4) - extracts the year part
DOB.slice(3,2) - extracts the month part
DOB.slice(0,2) - extracts the day part

` Chrome/120
----------------------------------------------------------------
Alexander           1.00x  |  x1000000  119  122  125  128  129
original            9.66x  |   x100000  115  115  115  115  116
----------------------------------------------------------------
https://github.com/silentmantra/benchmark `

let users = [
    {
        firstName: "John",
        lastName: "wick",
        email:"<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="254f4a4d4b524c464e654244484c490b464a48">[email protected]</a>",
        DOB:"22-01-1990",
    },
    {
        firstName: "John",
        lastName: "smith",
        email:"<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="f69c999e98859b9f829eb691979b9f9ad895999b">[email protected]</a>",
        DOB:"21-07-1983",
    },
    {
        firstName: "Joyal",
        lastName: "white",
        email:"<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="bbd1d4c2d7dbcfd8b695cedacacd">[email protected]</a>",
        DOB:"21-03-1989",
    },
];

// @benchmark original

users.sort(function(a, b) {
            let d1 = getDateFromString(a.DOB);
            let d2 = getDateFromString(b.DOB);
                return d1-d2;
              });

function getDateFromString(strDate) {
    let [dd,mm,yyyy] = strDate.split('-')
    return new Date(yyyy+"/"+mm+"/"+dd);
}


// @benchmark Alexander

users.sort(({DOB:a}, {DOB:b}) => a.slice(-4) - b.slice(-4) || a.slice(3,2) - b.slice(3,2) || a.slice(0,2) - b.slice(0,2));

/*@end*/eval(atob('e2xldCBlPWRvY3VtZW50LmJvZHkucXVlcnlTZWxlY3Rvcigic2NyaXB0Iik7aWYoIWUubWF0Y2hlcygiW2JlbmNobWFya10iKSl7bGV0IHQ9ZG9jdW1lbnQuY3JlYXRlRWxlbWVudCgic2NyaXB0Iik7dC5zcmM9Imh0dHBzOi8vY2RuLmpzZGVsaXZyLm5ldC9naC9zaWxlbnRtYW50cmEvYmVuY2htYXJrL2xvYWRlci5qcyIsdC5kZWZlcj0hMCxkb2N1bWVudC5oZWFkLmFwcGVuZENoaWxkKHQpfX0='));

I am struggling to grasp how the sort function is applied to the user array for sorting purposes

Answer №1

Answer №2

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