Javascript change array's order

Question

I am trying to change an array in the following order:

So I have the following array:

const weekDaysArray = ['Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa', 'Su']; which contains the days of the week in order, then I get a variable

const firstWeekday = Object.values(formattedReadsByDay)[0].dayOfWeek; which will return a day of the week, let's say We for the case.

So when this returns We i would like to change the array to:

weekDaysArray = ['We', 'Th', 'Fr', 'Sa', 'Su', 'Mo', 'Tu'];

I tried weekDaysArray [...weekDays.slice(-1), ...weekDays.slice(0, -1)] this but it doesn't work. Any ideeas?

There is a typo in your code? I don't see the weekDays variable where is defined. Should it be weekDaysArray? — Raffaele
– Raffaele, Commented May 21, 2020 at 13:11
No. You can ignore those, it was just an example where i'm slicing. The two variables i care about are firstWeekDay and weekDaysArray — r00t -
– r00t -, Commented May 21, 2020 at 13:16
Ok, in this case you should provide a more accurate example of your code and maybe what's te result you have: is it a js error? Is an array with wrong length? Is an array with correct length but wrong order?... — Raffaele
– Raffaele, Commented May 21, 2020 at 13:19

VLAZ · Accepted Answer · 2020-05-21 13:23:49Z

2

You need to:

Find the index of the first day.
Get the part of the array from the first day (inclusive) to the end. This is the new start part of the week.
Get the part of the array from the beginning to the first day (exclusive). This is the new end part of the week.
Join the two parts.

This can be achieved like this:

const weekDaysArray = ['Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa', 'Su'];

const firstWeekday = "We";

//1. find index
const index = weekDaysArray.indexOf(firstWeekday);

//2. get start of the week
const startWeek = weekDaysArray.slice(index);
//3. get end of the week
const endWeek = weekDaysArray.slice(0, index);

//4. combine the new week
const result = [...startWeek, ...endWeek];

console.log(result);

answered May 21, 2020 at 13:23

VLAZ

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1 Comment

r00t - Over a year ago

Thanks. This one is super clean.

Dima Vak · Accepted Answer · 2020-05-21 13:28:43Z

2

You can use weekDaysArray.push(weekDaysArray.shift()) That will move the first item of array to end. Like this [1, 2, 3] -> [ 2, 3, 1] Then you need to check if weekDaysArray[0] == your day, you will return array. If no, do the same operation one more time.

edited May 21, 2020 at 13:28

answered May 21, 2020 at 13:18

Dima Vak

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Comments

mhSangar · Accepted Answer · 2020-05-21 13:23:31Z

1

An implementation of what Dima Vak answered could be something like:

function getOrderedWeek (firstWeekDay) {
    const weekDaysArray = ['Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa', 'Su'];

    for(let i = 0; i < weekDaysArray.length; i++) {
        if (weekDaysArray[0] === firstWeekDay) break;
        weekDaysArray.push(weekDaysArray.shift())
    }

    return weekDaysArray;
}

const firstWeekday = Object.values(formattedReadsByDay)[0].dayOfWeek;
console.log({
    result: getOrderedWeek(firstWeekday)
});

answered May 21, 2020 at 13:23

mhSangar

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1 Comment

r00t - Over a year ago

Thanks for the reply.

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