How to get a value from multiple arrays by the index?

Question

I want to get the fifth values in each array inside the Board array.

const BOARD = [            ↓
    [ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'],
    [ '5', '5', '5', '5', '5', '9', 'B', 'B', 'C', 'D', 'E', 'F', 'F', '1', '2', '3'],
    [ '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7'],
    [ 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B'],
    [ '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0'],
    [ '5', 'A', 'A', 'A', 'A', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4'],
    [ '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8'],
    [ 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C'],
    [ '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1'],
    [ '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5'],
    [ 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'],
    [ 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D'],
    [ '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2'],
    [ '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6'],
    [ 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A'],
    [ 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E'],
];

I have tried:

function getFifthRow () {
    BOARD.forEach((l) => {
        console.error(l[6])
    })
}

But got UNDEFINED. why is that?

Thanks!!

Use array index `4` to get the fifth value in each array. (not `6`) — Wyck, Jul 07 '21 at 19:37
Also, just in case it's relevant, your `getFifthRow` doesn't _return_ a value, it just _logs_ a value. — Wyck, Jul 07 '21 at 19:39

score 0 · Accepted Answer · answered Jul 07 '21 at 19:35

You can use Array#map to get a new array containing the fifth elements of each inner array. Note that arrays are zero-indexed, so the fifth value is at index 4.

const BOARD = [            
    [ '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'],
    [ '5', '5', '5', '5', '5', '9', 'B', 'B', 'C', 'D', 'E', 'F', 'F', '1', '2', '3'],
    [ '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7'],
    [ 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B'],
    [ '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0'],
    [ '5', 'A', 'A', 'A', 'A', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4'],
    [ '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8'],
    [ 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C'],
    [ '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1'],
    [ '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5'],
    [ 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'],
    [ 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D'],
    [ '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2'],
    [ '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6'],
    [ 'B', 'C', 'D', 'E', 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A'],
    [ 'F', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E'],
];
let res = BOARD.map(r => r[4]);
console.log(res);

How to get a value from multiple arrays by the index?

1 Answers1