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.

Answer 1

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); 

Answer 2

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); 

Answer 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)); 

Answer 4

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.