Fill remaining array index with null based on the length specified

Question

I have list of arrays with different length. I want to find the highest length of the array in the list and make all remaining arrays of same length by filling null/empty value.

e.g: I have a list of array

[ [1,2,2,4,4], [2,3,2,4], [2,4,21,4], [1,2]];

I want to find the highest length of array in the list i.e 5 in above case ( length of [1,2,2,4,4])

I want to make all remaining arrays also of same length like below

[ [1,2,2,4,4], [2,3,2,4,''], [2,4,21,4,''], [1,2,'','','']];

How can I achieve that?

Sample code of list of array and finding max length

let data = [ [1,2,2,4,4],
[2,3,2,4], [2,4,21,4], [1,2]
];

const length = Math.max(...(data.map(el => el.length)));

console.log('array list', data);
console.log('max length', length);

Nina Scholz · Accepted Answer · 2020-09-18 13:26:36Z

3

You could iterate the array and push empty strings until the wanted length.

const
    data = [[1, 2, 2, 4, 4], [2, 3, 2, 4], [2, 4, 21, 4], [1, 2]],
    length = Math.max(...data.map(({ length }) => length));

data.forEach(a => {
    while (a.length < length) a.push('');
});

console.log('max length', length);
console.log('array list', data);

If you like to get a new array, you could map new arrays.

const
    data = [[1, 2, 2, 4, 4], [2, 3, 2, 4], [2, 4, 21, 4], [1, 2]],
    length = Math.max(...data.map(({ length }) => length)),
    result = data.map(a => Array.from({ length }, (_, i) => i < a.length ? a[i] : ''));

console.log('max length', length);
console.log('array list', result);

answered Sep 18, 2020 at 13:26

Nina Scholz

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Comments

Nick · Accepted Answer · 2020-09-18 13:31:46Z

2

You can concat an array filled with null values to each entry in data:

let data = [ [1,2,2,4,4],
[2,3,2,4], [2,4,21,4], [1,2]
];

const length = Math.max(...(data.map(el => el.length)));

data = data.map(a => a.concat(new Array(length - a.length).fill(null)));

console.log('array list', data);
console.log('max length', length);

answered Sep 18, 2020 at 13:31

Nick

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Comments

Kevin.a · Accepted Answer · 2020-09-18 13:26:50Z

2

let data = [ [1,2,2,4,4],
[2,3,2,4], [2,4,21,4], [1,2]
];

const length = Math.max(...(data.map(el => el.length)));

data.forEach(item => {
    while (item.length < length){
        item.push(''); 
    }
})

console.log(data)

answered Sep 18, 2020 at 13:26

Kevin.a

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