How to remove one subset from an array in JS?

Question

Let's say I have an array such as: [1, 1, 2, 2, 3, 3, 4, 5]
And I want to remove this array of elements [1, 2, 3, 4, 5]
So in the end I want to be left with [1, 2, 3]

I have tried using the method below but it removes all copies of the elements from the main array.

myArray = myArray.filter( function( el ) {
  return !toRemove.includes( el );
} );

create an object that will have first array values as keys and number of that values as value, forEach the second array and substract 1 from each key from first array — AndrewShmig
– AndrewShmig, Commented Feb 10, 2019 at 16:31
"And I want to remove this array of elements" Do you mean remove the elements from the original array or return a new array containing only the elements not included within toRemove? Is myArray = myArray.filter() intentionally redefining myArray as the result of .filter(), which returns a new array? — guest271314
– guest271314, Commented Feb 10, 2019 at 16:33

jo_va · Accepted Answer · 2019-02-10 17:38:46Z

2

Here is a way to do it using filter, indexOf and splice.

const input = [1, 1, 2, 2, 3, 3, 4, 5];

function removeSubset(arr, subset) {
  const exclude = [...subset];
  return arr.filter(x => {
    const idx = exclude.indexOf(x);
    if (idx >= 0) {
      exclude.splice(idx, 1);
      return false;
    }
    return true;
  });
}

console.log(removeSubset(input, [1, 2, 3, 4, 5]));

answered Feb 10, 2019 at 17:38

jo_va

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Comments

Nina Scholz · Accepted Answer · 2019-02-10 16:53:34Z

1

You could get a Map and count the values and filter by checking the count and decrement the count if found.

var array = [1, 1, 2, 2, 3, 3, 4, 5],
    remove = [1, 2, 3, 4, 5],
    map = remove.reduce((m, v) => m.set(v, (m.get(v) || 0) + 1), new Map),
    result = array.filter(v => !map.get(v) || !map.set(v, map.get(v) - 1));

console.log(result);

edited Feb 10, 2019 at 16:53

answered Feb 10, 2019 at 16:34

Nina Scholz

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3 Comments

Shidersz Over a year ago

And where is the array of the elements to remove? What is just want to remove elements [1,2]?

Mark Over a year ago

This now only works if the removal array is sorted, which is why I asked about it in the comment.

Mark Over a year ago

Ja, that seems like the most reasonable way to do this without getting quadratic complexity.

Shidersz · Accepted Answer · 2019-02-10 17:00:55Z

One solution is looping on the array of elements to remove and for each one remove the first element found on the input array:

const input = [1, 1, 2, 2, 3, 3, 4, 5];

const removeItems = (input, items) =>
{
    // Make a copy, to not mutate the input.
    let clonedInput = input.slice();

    // Search and remove items.
    items.forEach(x =>
    {
        let i = clonedInput.findIndex(y => y === x);
        if (i >= 0) clonedInput.splice(i, 1);
    });
    
    return clonedInput;
}

console.log(removeItems(input, [1,2,3,4,5]));
console.log(removeItems(input, [1,2]));
console.log(removeItems(input, [1,99,44,5]));

If you still want to use filter, you can use the items to remove as the this argument of the filter, something like this:

const input = [1, 1, 2, 2, 3, 3, 4, 5];

const removeItems = (input, items) =>
{        
    return input.filter(function(x)
    {
        let i = this.findIndex(y => y === x);
        return i >= 0 ? (this.splice(i, 1), false) : true;
    }, items.slice());
}

console.log(removeItems(input, [1,2,3,4,5]));
console.log(removeItems(input, [1,2]));
console.log(removeItems(input, [1,99,44,5]));

Code Maniac · Accepted Answer · 2019-02-10 17:04:25Z

1

You can use Filter and Shitf and Sort

let arr = [1, 1, 2, 2, 3, 3, 4, 5]
let remove  = [1, 3, 2, 4, 5].sort((a,b)=>a-b)

let op = arr.sort((a,b)=>a-b).filter(e => ( remove.includes(e) ? (remove.shift(), false) : true ))


console.log(op)

edited Feb 10, 2019 at 17:04

answered Feb 10, 2019 at 16:33

Code Maniac

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