Javascript: Filter Array with duplicate Dates

Question

I´m using Angular2 and I have an array with Date-Objects (~1000). Most of the Date-Objects have got the exactly same dates (for example 2016_11_02; Dates have no hours & minutes). Normally there should be about ~10-20 different Dates in the Array.

Now i want to filter this array and delete the duplicate Dates. So in the end there should be about ~10-20 Date-Objects in the array.

Here´s the code i tried:

let uniqueArray = duplicatesArray.filter(function(elem, pos) {
            return channelEPGDates.indexOf(elem) == pos;
        });
        console.log('unique: ' + uniqueArray.length);

I know this is not correct, cause the unique-Array has the same length as the old array. But how can i compare the Dates itself in the filter-function?

Thanks so much!

If you want to be efficient about it, and you are only on newer browsers, then Array.reduce is a good bet. — Emil S. Jørgensen
– Emil S. Jørgensen, Commented Nov 4, 2016 at 8:55

Gregor Menih · Accepted Answer · 2016-11-04 09:15:36Z

13

I would map the dates to epoch time using the getTime method, and then map them back to Date objects.

let uniqueArray = duplicatesArray
.map(function (date) { return date.getTime() })
.filter(function (date, i, array) {
    return array.indexOf(date) === i;
 })
.map(function (time) { return new Date(time); });

edited Nov 4, 2016 at 9:15

answered Nov 4, 2016 at 8:55

Gregor Menih

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2 Comments

Junias Over a year ago

perfect, thanks! This is a good, short solution! Could you please update your answer to '.filter(function (date, i, array) {', then i can mark it ;)

Gregor Menih Over a year ago

Oops, nice catch. Fixed :)

Nina Scholz · Accepted Answer · 2019-11-20 13:47:48Z

3

You could use Set and the spread syntax ... for it.

unique = src => [...new Set(src)];

var unique = src => [...new Set(src)];
    array = ["Mike", "Matt", "Nancy", "Adam", "Jenny", "Nancy", "Carl"];

console.log(unique(array));

To get objects with unique dates, you could filter the data by using a closure over a Set and a callback for getting the part which has to be unique.

var unique = (src, fn) => src.filter((s => o => !s.has(fn(o)) && s.add(fn(o)))(new Set));
    array = [{ date: new Date('2019-11-01')}, { date: new Date('2019-11-01')}, { date: new Date('2019-11-01')}, { date: new Date('2019-11-02')}, { date: new Date('2019-11-01')}, { date: new Date('2019-11-05')}, { date: new Date('2019-11-05')}, { date: new Date('2019-11-04')}, { date: new Date('2019-11-07')}];

console.log(unique(array, ({ date }) => date.toISOString().slice(0, 10)));

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edited Nov 20, 2019 at 13:47

answered Nov 4, 2016 at 9:05

Nina Scholz

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2 Comments

Nina Scholz Over a year ago

@SergeyReutskiy, of course it's working with objects as well, but only with same object reference. as i see the data is a string and not an object, which works well with map. if there are objects, then a stringed item would help.

qasimalbaqali Over a year ago

The answer you provided, yes it's meant to remove duplicates and it's actually a very nice way in doing it, but it doesn't answer OPs question since he is asking about removing Date objects specifically. Unless of course as you stated they have the same reference. How about if they don't? How do you remove duplicate Date objects that share the same values but not the same references.

Bhupinder kumar · Accepted Answer · 2016-11-04 08:53:48Z

0

You can do with jQuery like this :

var names = ["Mike","Matt","Nancy","Adam","Jenny","Nancy","Carl"];
var uniqueNames = [];
$.each(names, function(i, el){
    if($.inArray(el, uniqueNames) === -1) uniqueNames.push(el);
});

answered Nov 4, 2016 at 8:53

Bhupinder kumar

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Comments

Cerbrus · Accepted Answer · 2016-11-07 10:02:27Z

-1

Here is a method using the built-in methods on Array.

var arr = ["John", "Jimmy", "John"];
var dArr = []; //Date array
while (dArr.length < 10000) { //Load a lot of pseudo dates
  dArr.push(
    new Date().getTime() + Math.round(Math.random() * 10)
  );
}

function arrayUnique(arr) {
  return arr.reduce(function(previousValue, currentValue) {
    if (previousValue.some(function(value, index) {
      return value === currentValue;
    }) === false) {
      previousValue.push(currentValue);
    }
    return previousValue;
  }, []);
}

console.log(arrayUnique(arr));
console.log(arrayUnique(dArr).sort());

edited Nov 7, 2016 at 10:02

Cerbrus

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answered Nov 4, 2016 at 9:04

Emil S. Jørgensen

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