Remove an item from an array by value, but leave the duplicates of that item

Question

I have a very simple array like this:

array = [1, 1, 6, 7, 9, 6, 4, 5, 4];

I need to be able to remove a value, but I need to remove only one value if there's duplicate values. So if I remove the value 6, the array should become:

array = [1, 1, 7, 9, 6, 4, 5, 4];

The order of which one gets removed doesn't matter, so it could be the last no. 6 or the first no. 6. How can I do this?

Edit I see there's a lot of confusion about why I need this, which results in incorrect answers. I'm making a Sudoku game and when a user inserts a number in a cell, the game has to check if the chosen number already occupies space in the same row or column. If so, the number of that specific row/column is added to this array. However, when a user fixes a mistake, the number of the row/column should be removed. A user can, however, make multiple mistakes in the same row or column, which is why I need to retain the duplicates in the array. Otherwise, users can make multiple mistakes in a row/column, and only fix one, and then the code will think there are no errors whatsoever anymore.

Hope this makes things more clear.

Possible duplicate of How do I make an array with unique elements (i.e. remove duplicates)? — CroMagnon
– CroMagnon, Commented Dec 29, 2016 at 14:53
And what is criteria for removing/keeping? Why '1' isn't removed? Ah, you will provide element as param... — sinisake
– sinisake, Commented Dec 29, 2016 at 14:55
@erol_smsr, I think that answers bellow aren't right. First, var should be checked - if unique - keep it, if duplicate - remove it (but just one occurence), right? — sinisake
– sinisake, Commented Dec 29, 2016 at 15:01

Suren Srapyan · Accepted Answer · 2016-12-29 14:55:33Z

4

Try to get the index of your item with indexOf() and then call splice()

let array = [1, 1, 6, 7, 9, 6, 4, 5, 4];
let index = array.indexOf(6);
array.splice(index,1);
console.log(array);

edited Dec 29, 2016 at 14:55

answered Dec 29, 2016 at 14:54

Suren Srapyan

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3 Comments

erol_smsr Over a year ago

Can I remove an item by its value instead of its index?

Suren Srapyan Over a year ago

@erol_smsr no you can't. You need to get the index and remove by index

kind user Over a year ago

That's a very weak, static solution. Look at the Kukkuz's code.

LellisMoon · Accepted Answer · 2016-12-29 15:06:59Z

3

var array=[1, 1, 6, 7, 9, 6, 4, 5, 4],
    removeFirst=function(val,array){
      array.splice(array.indexOf(val),1)
        return array;
    };

console.log(removeFirst(6,array));

answered Dec 29, 2016 at 15:06

LellisMoon

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4 Comments

kukkuz Over a year ago

@erol_smsr if I may, this does not check if it has a duplicate before removing the element?

erol_smsr Over a year ago

Yeah it doesn't check it, but does it have to? I tested it in the console and the result is exactly what I need: var array = [1,2,7,7,9,10,9] undefined array.splice(array.indexOf(7), 1); [7] array [1, 2, 7, 9, 10, 9] As you can see, it removed one instance of number 7 from the array. You think the check has to be performed?

kukkuz Over a year ago

Yes I do think so, for instance for var array=[1, 1, 6, 7, 9, 6, 4, 5, 4] try removeFirst(7) and it will result in [1, 1, 6, 9, 6, 4, 5, 4]...

erol_smsr Over a year ago

That's okay. If a number only occurs once in the array, it should also be removed. Thanks for double-checking though :)

kukkuz · Accepted Answer · 2016-12-29 15:26:54Z

3

You can use Array.prototype.findIndex to find the first index at which the element to be removed appears and then splice it.

Also you can create a hastable to ascertain that we remove only if a duplicate is availabe - see demo below:

var array = [1, 1, 6, 7, 9, 6, 4, 5, 4];

var hash = array.reduce(function(p,c){
  p[c] = (p[c] || 0) + 1;
  return p;
},{});

function remove(el) {
  if(hash[el] < 2)
     return;
  array.splice(array.findIndex(function(e) {
    return e == el;
  }), 1);
}

remove(6);
remove(7);
console.log(array);

edited Dec 29, 2016 at 15:26

answered Dec 29, 2016 at 14:56

kukkuz

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Comments

sinisake · Accepted Answer · 2016-12-29 15:34:38Z

1

If order of removed element (not elements!) isn't important, you can use something like this:

array = [1, 1, 6, 7, 9, 6, 4, 5, 4];
function remove_if_dupe(elem, array) {
dupes=[];
for(i=0;i<array.length;i++) {
if(array[i] === elem) {
dupes.push(elem);
}

}
if(dupes.length>1) {
//is duplicated
array.splice(array.indexOf(elem), 1);
}
return array;
}

console.log(remove_if_dupe(6,array));

This should keep unique elements, hopefully.

edited Dec 29, 2016 at 15:34

answered Dec 29, 2016 at 15:19

sinisake

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