根据当前日期排序数组

Question

I am trying to re-order the array below given todays date:

[
    {
        "index": "0",
        "day": "Monday",
        "food": "Salad"
    },
    {
        "index": "1",
        "day": "Friday",
        "food": "Pasta"
    },
    {
        "index": "2",
        "day": "Sunday",
        "food": "Pasta"
    },
    {
        "index": "3",
        "day": "Thursday",
        "food": "Pasta"
    },
    {
        "index": "4",
        "day": "Tuesday",
        "food": "Pasta"
    },
    {
        "index": "2",
        "day": "Sunday",
        "food": "Pasta"
    },
    {
        "index": "5",
        "day": "Wednesday",
        "food": "Pasta"
    },
    {
        "index": "6",
        "day": "Saturday",
        "food": "Pasta"
    }
]

Say today is Saturday , after ordering, the expected output by item index is: 6, 2, 2, 0, 4, 5, 3, 1 If today was Tuesday , the output by index is: 4, 5, 3, 1, 6, 2, 2, 0

I am using moment.js , and so far I am failing to create a non bulky code for this. Eventually I would like to wrap the code in a custom orderBy filter to be used on a ng-repeat directive.

Answer 1

Here's the minimal solution I came up with:

const DAYS = { 'Sunday': 0, 'Monday': 1, 'Tuesday': 2, 'Wednesday': 3, 'Thursday': 4, 'Friday': 5, 'Saturday': 6 };

// Get the relative index of a day using today as a reference.
function relativeIndex(day) {
  const TODAY = new Date().getDay();
  return (DAYS[day] - TODAY + 7) % 7;
}

// Sort a lit of data starting by today.
function sort(data) {
  return data.sort((a, b) => relativeIndex(a.day) - relativeIndex(b.day));
}

The key here is the relativeIndex function which calculates the index of any day using today as a reference.

Answer 2

Sorting by today was a little tricky to achieve just using sort. To overcome it we are creating an array of days, then resorting that so the current day is at index 0, then sorting your calendar array based on the sorted days.

to avoid having to calculate the sortedDays multiple times, it's wrapped in a closure that returns the function that will sort the given array.

It's immutable so you won't need to change the original order if you don't need to.

 const calendar=[{index:"0",day:"Monday",food:"Salad"},{index:"1",day:"Friday",food:"Pasta"},{index:"2",day:"Sunday",food:"Pasta"},{index:"3",day:"Thursday",food:"Pasta"},{index:"4",day:"Tuesday",food:"Pasta"},{index:"2",day:"Sunday",food:"Pasta"},{index:"5",day:"Wednesday",food:"Pasta"},{index:"6",day:"Saturday",food:"Pasta"}]; const sortByToday = (function() { const date = new Date() const today = date.getDay() const days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'] const sortedDays = [ ...days.slice(today), ...days.slice(0, today) ] return function(calendar) { return calendar.slice().sort((a, b) => { return sortedDays.indexOf(a.day) > sortedDays.indexOf(b.day) }) } })() console.log( sortByToday(calendar) ) 

Answer 3

Given 'menu' as given array, use customized comparison to sort:

var map = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
var day = (new Date()).getDay();
menu.sort(function(a, b){
    var aDay = map.indexOf(a.day), bDay = map.indexOf(b.day);
    return (aDay - bDay) * 
        (day <= Math.min(aDay, bDay) || day > Math.max(aDay, bDay) ? 1 : -1);
});

for(var i=0; i<menu.length; ++i){
  console.log(menu[i].index);
}

Answer 4

Using Date() gymnastics. Scroll down to see commented code.

 let arr = [ { "index": "0", "day": "Monday", "food": "Salad" }, { "index": "1", "day": "Friday", "food": "Pasta" }, { "index": "2", "day": "Sunday", "food": "Pasta" }, { "index": "3", "day": "Thursday", "food": "Pasta" }, { "index": "4", "day": "Tuesday", "food": "Pasta" }, { "index": "2", "day": "Sunday", "food": "Pasta" }, { "index": "5", "day": "Wednesday", "food": "Pasta" }, { "index": "6", "day": "Saturday", "food": "Pasta" } ] // first create an array to label days let dayOfWeekLabels = [ 'Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday' ]; let days = []; let runningDate = new Date(); // optional offset for debugging / testing //runningDate.setDate( runningDate.getDate()+1 ); // now create an array that rearranges the first array // according to what day it is today dayOfWeekLabels.forEach((label,i) => { days.push( dayOfWeekLabels[new Date(runningDate).getDay()] ); runningDate.setDate( runningDate.getDate()+1 ); }); // now enhance the original array with an "order" value let orderedArr = arr.map(obj => { obj.order = days.indexOf(obj.day); return obj; }); // now sort based on the "order" value orderedArr.sort((a,b) => { return (a.order - b.order); }); /* console.log(orderedArr); */ document.getElementById('output').innerHTML = JSON.stringify(orderedArr,null," "); 

 <pre><code class="json" id="output"></code></pre>