Javascript: How to remove only one value from duplicate array values

Question

I have an array ['2530491','2530491','2530491','2530492'] the 2530491 is duplicated thrice, and I want to remove a single value of 2530491 from 3 of them, so the output would be like : ['2530491','2530491','2530492'].

fileArrayAnnounce_size = jQuery.grep(fileArrayAnnounce_size, function(value){
  return value != file_size.metas[0].size;
});

I try grip but it removes all value which same. I want to remove only a single value from duplicates.

http://stackoverflow.com/questions/18008025/remove-duplicate-item-from-array-javascript — SKARVA Bodavula, Apr 20 '17 at 14:25
what are the rules exactly....allow 2 duplicates but no more? — charlietfl, Apr 20 '17 at 14:26
@charlietfl that seems to be the case. Twice but not thrice. — evolutionxbox, Apr 20 '17 at 14:27
Even more than 2 duplicates as long as I removed a single of it. Just to remove single value from duplicate regardless how many duplicates — HiFlyer Ojt, Apr 20 '17 at 14:28
So if there are four of the same, you still only wan't to remove one item? May you clarify the rules? — evolutionxbox, Apr 20 '17 at 14:28
@evolutionxbox but no it's not clear and needs to be stated as there are different ways to interpret still — charlietfl, Apr 20 '17 at 14:28

tymeJV · Answer 1 · 2017-04-20T14:28:22.553

5

You can use splice and indexOf to remove the first instance:

fileArrayAnnounce_size.splice(fileArrayAnnounce_size.indexOf('2530491'), 1)

A safer way:

var index = fileArrayAnnounce_size.indexOf('2530491')
if (index > -1) {
    fileArrayAnnounce_size.splice(index, 1);
}

Check and remove duplicates:

var mapOfValues = fileArrayAnnounce_size.reduce(function(vals, current) {
    if (vals[current]) {
        vals[current]++;
    } else {
        vals[current] = 1;
    }

    return vals;
}, {});

And now check and remove anything with more than 1 value:

for (var value in mapOfValues) {
    if (mapOfValues[value] > 1) {
        var idx = fileArrayAnnounce_size.indexOf(value);
        fileArrayAnnounce_size.splice(idx, 1);
    }
}

Demo: https://jsfiddle.net/1277mxt9/

edited Apr 20 '17 at 14:28

answered Apr 20 '17 at 14:23

tymeJV

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Don't you also need a check as to whether a value has a duplicate? Otherwise all values would be removed. – evolutionxbox Apr 20 '17 at 14:25
2

don't see how this verifies a duplicate exists – charlietfl Apr 20 '17 at 14:25
I mean, this works _but_ only if you know the duplicate values. – George Apr 20 '17 at 14:26
Updated the code to find duplicates or more, and then a way to remove 1 of each of those values – tymeJV Apr 20 '17 at 14:28
OP has changed the requirements again... remove one, and only one, duplicate item from a set of duplicate items, no matter how many. 3 dupes become 2, 4 dupes become 3, etc. – evolutionxbox Apr 20 '17 at 14:30
@evolutionxbox that's all that the edit does ...remove one instance – charlietfl Apr 20 '17 at 14:31
1

Pretty sure the edit above works fine @evolutionxbox – tymeJV Apr 20 '17 at 14:32

kind user · Accepted Answer · 2017-04-20T15:04:18.300

2

You could check if given element has dupe elements or not, if so - remove just one duplicate entry of specified element from the original array.

var arr = ['2530491','2530491','2530491','2530492'],
    hash = [...new Set(arr)];
    hash.forEach((v,i) => arr.indexOf(v) != arr.lastIndexOf(v) ? arr.splice(arr.indexOf(v), 1) : null);
    
    console.log(arr);

edited Apr 20 '17 at 15:04

answered Apr 20 '17 at 14:33

kind user

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I like the simplicity – HiFlyer Ojt Apr 20 '17 at 14:46

score 1 · Answer 3 · answered Apr 20 '17 at 14:42

You can use filter() and pass one object as thisArg parameter to use it as hash table.

var data = ['2530491','2530491','2530491','2530492', '2530492'];

var result = data.filter(function(e) {
  if(!this[e]) this[e] = 1
  else if (this[e] == 1) return this[e] = 2, false
  return true;
}, {})

console.log(result)

Javascript: How to remove only one value from duplicate array values

3 Answers3

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