how to remove or insert into a Javascript multidimensional array

Question

I have a 2-dimensional data structure like this:

    var arr = [
        {
            'subarr': [
                { 'a': '11' },
                { 'a': '12' }
            ]
        },
        {
            'subarr': [
                { 'a': '21' },
                { 'a': '22' }
            ]
        },
        {
            'subarr': [
                { 'a': '31' },
                { 'a': '32' }
            ]
        }
    ];

I need to insert an element, e.g. '23', or remove, e.g. '22'.

The slice method does not copy the entire data, but inserts or removes in the array 'in place'. But how do I apply that on a 2-dim array? This code will not work, because the [i] operation creates a new variable, so arr will not be changed at all:

arr[1].subarr.slice(0, 1);

I would need some reference type of variable to point at the subarray to be sliced.

Any help would be appreciated

As happens more often: the complicated problem has a simple answer. I should have used splice(), not slice(), as the answers told me.

Emeeus · Accepted Answer · 2018-06-19 13:19:44Z

2

To add push(), [], splice() or unshift()

arr[1].subarr.push({'a':'23'}); //add at the end

or

arr[1].subarr.unshift({'a':'23'}); //add in the beginig

to add at specific position (2th in this case)

arr[1].subarr.splice(2, 0, {'a':'433'}, {'a':'544'});

to remove splice

arr[1].subarr.splice(1,1); //splice(start,deleteCount)

edited Jun 19, 2018 at 13:19

answered Jun 19, 2018 at 13:08

Emeeus

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7 Comments

Roland Kwee Over a year ago

Thanks, but your solutions will return only the 2nd arr element, with the modified data. The variable 'arr' will not be changed.

Roland Kwee Over a year ago

Anything that starts with arr[i] will obviously not work. I need a solution for the problem of changing the variable arr.

Emeeus Over a year ago

@Roland arr[1].subarr.slice(0, 1); modifies arr

Hikmat G. Over a year ago

splice will actually modify your array not slice;

Emeeus Over a year ago

@Hikmat yes it's arr[1].subarr.splice(0, 1); I made a mistake in the comment

|

Niladri Basu · Accepted Answer · 2018-06-19 13:49:47Z

How to insert an element ie '23' without mutation:

    var arr = [
        {
            'subarr': [
                { 'a': '11' },
                { 'a': '12' }
            ]
        },
        {
            'subarr': [
                { 'a': '21' },
                { 'a': '22' }
            ]
        },
        {
            'subarr': [
                { 'a': '31' },
                { 'a': '32' }
            ]
        }
    ];
    
    var newArr = [...arr, arr[0].subarr.push({'a':'23'})]
    console.log(newArr)

How to remove an element ie '22' without mutation:

    var arr = [
        {
            'subarr': [
                { 'a': '11' },
                { 'a': '12' }
            ]
        },
        {
            'subarr': [
                { 'a': '21' },
                { 'a': '22' }
            ]
        },
        {
            'subarr': [
                { 'a': '31' },
                { 'a': '32' }
            ]
        }
    ];

var newArr = [...arr.map(element => element.subarr.filter(item => item.a !== '22'))]

console.log(newArr)

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