Find missing day from array of dates javascript

Question

I am getting an array of day dates from an API:

0:{date: "2016-11-17T00:00:00",…}
1:{date: "2016-11-18T00:00:00",…}
2:{date: "2016-11-19T00:00:00",…}
3:{date: "2016-11-21T00:00:00",…}
4:{date: "2016-11-22T00:00:00",…}
5:{date: "2016-11-23T00:00:00",…}

In this example the array is missing this date:

{date: "2016-11-20T00:00:00",…}

What is the best way to find a missing day from an array of dates in Javascript or Angular?

So that I later would be able to pass it to a datepicker as a disabled day.

Answer 1

Check this out:

1. First you can sort the array (in case it is not so) using Array.prototype.sort

2. Then use Array.prototype.reduce and a hash table to find the missing dates

Demo given in snippet below:

var array=[
  {date:"2016-11-17T00:00:00"},
  {date:"2016-11-19T00:00:00"},
  {date:"2016-11-18T00:00:00"},
  {date:"2016-11-21T00:00:00"},
  {date:"2016-11-22T00:00:00"},
  {date:"2016-11-23T00:00:00"},
  {date:"2016-11-27T00:00:00"}
];

var result = array.sort(function(a,b){
   return Date.parse(a.date) - Date.parse(b.date);
}).reduce(function(hash){
  return function(p,c){
    var missingDaysNo = (Date.parse(c.date) - hash.prev) / (1000 * 3600 * 24);
    if(hash.prev && missingDaysNo > 1) {
      for(var i=1;i<missingDaysNo;i++)
        p.push(new Date(hash.prev+i*(1000 * 3600 * 24)));
    }
    hash.prev = Date.parse(c.date);
    return p;
  };
}(Object.create(null)),[]);

console.log(result);

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Answer 2

Create a new array missingDates[]

Iterate over the array (from your API) using a for loop

for (i = 0; i < array.length; i++){
    var date1 = convert your array item (with index i) to a date
    var date2 = convert your array item (with index i + 1) to a date (keep in mind, index i + 1 cant be > than array.length)

    //calculate diffDays between the 2 dates, if diff is > 1, you have a missing date
    var missingDate = create your missing date (use your date1 variable + 1Day)

    //add misingDate to missingDates[] array
    missingDates.push(missingDate)
}

Answer 3

You can do a method getMissingDate to return null if there is not missing date or return the Date object if there is a difference between to dates bigger than one day:

var arr1 = [{date: "2016-11-17T00:00:00"}, {date: "2016-11-18T00:00:00"}, {date: "2016-11-19T00:00:00"}, {date: "2016-11-21T00:00:00"}, {date: "2016-11-22T00:00:00"}, {date: "2016-11-23T00:00:00"}],
    arr2 = [{date: "2016-11-17T00:00:00"}, {date: "2016-11-18T00:00:00"}, {date: "2016-11-19T00:00:00"}, {date: "2016-11-20T00:00:00"}, {date: "2016-11-21T00:00:00"}, {date: "2016-11-22T00:00:00"}, {date: "2016-11-23T00:00:00"}],
    getMissingDate = function(arr) {
      var result = null;
      for (var i = 0, l = arr.length - 1; i < l; i++) {
        var current = new Date(arr[i].date),
            next = new Date(arr[i + 1].date);

        if (1 < Math.ceil(Math.abs(next.getTime() - current.getTime()) / (1000 * 3600 * 24))) {
          result = new Date(current.setDate(current.getDate() + 1));
          break;
        } 
      }

      return result;
    };

console.log('arr1:', getMissingDate(arr1));
console.log('arr2:', getMissingDate(arr2));

Answer 4

var array=[
  {date:"2016-01-01T00:00:00"},
  {date:"2016-03-01T00:00:00"},
  {date:"2016-04-01T00:00:00"},
  {date:"2016-07-01T00:00:00"},
  {date:"2016-09-01T00:00:00"},
  {date:"2016-11-01T00:00:00"},
  {date:"2016-12-01T00:00:00"}
];

var result = array.sort(function(a,b){
   return Date.parse(a.date) - Date.parse(b.date);
}).reduce(function(hash){
  return function(p,c){
    var missingMonthsNo= (Date.parse(c.date) - hash.prev) / (1000 * 3600 * 24);
    if(hash.prev && missingMonthsNo> 1) {
      for(var i=1;i<missingMonthsNo;i++)
        p.push(new Date(hash.prev+i*(1000 * 3600 * 24)));
    }
    hash.prev = Date.parse(c.date);
    return p;
  };
}(Object.create(null)),[]);

console.log(result);

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