CODEWITHSUNDEEP
javascriptarraysmultidimensional-array
bronkula
bronkula

Reputation: 652

Convert a single dimensional array into a multidimensional array

In Javascript, how to convert a single dimensional array into a multidimensional array of unspecified depth or length.

Example:

let input = ['a','b','b','b','a','a','b','b','b','c','c','a','a','b','b'];
const makeMatrix = () => {}

let output = makeMatrix(input);

// output: ['a',['b','b','b'],'a','a',['b','b','b',['c','c']],'a','a',['b','b']]

What should the makeMatrix function look like to accomplish this task? Assume that values always move in a linear forward direction, but might possibly cut backward. So a always leads to b. An a would never hop to c. But c might drop back down to a.

This is to try to convert heading elements into a table of contents. Making a simple single tier toc is easy, but making a multi tiered one is wracking my brain. I have looked through a number of solutions, but have not seen anything that solves this particular problem.

Upvotes: 4

Views: 269

Answers (3)

Jeto
Jeto

Reputation: 14927

Alternative version, using JSON building/parsing:

const input = ['a', 'b', 'b', 'b', 'a', 'a', 'b', 'b', 'b', 'c', 'c', 'a', 'a', 'b', 'b'];

const result = JSON.parse(Object.entries(input).reduce((json, [key, val]) => {
  const jsonVal = JSON.stringify(val);
  const diff = key > 0 ? val.charCodeAt(0) - input[key - 1].charCodeAt(0) : 0;
  if (diff > 0) {
    json += ',['.repeat(diff) + jsonVal;
  } else if (diff < 0) {
    json += ']'.repeat(-diff) + ',' + jsonVal;
  } else {
    json += (key > 0 ? ',' : '') + jsonVal;
  }
  return json;
}, '[') + ']'.repeat(input.slice(-1)[0].charCodeAt(0) - input[0].charCodeAt(0) + 1));

console.log(result);

This basically builds a JSON string using Array.reduce on the input array, adding each item and comparing key codes to include the right amount of opening/closing brackets in the process.

Upvotes: 2

Nina Scholz
Nina Scholz

Reputation: 386520

You could take a level variable and a levels array for pushing unknown elements.

var input = ['a', 'b', 'b', 'b', 'a', 'a', 'b', 'b', 'b', 'c', 'c', 'a', 'a', 'b', 'b'],
    levels = [[]],
    level = 0,
    result;

input.forEach(v => {
    var l = level;
    do {
        if (levels[l][0] === v) {
            level = l;
            levels[level].push(v);
            return;
        }
    } while (l--)
    levels[level].push(levels[level + 1] = [v]);
    level++;
});

result = levels[0][0];

console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }

Upvotes: 4

Countingstuff
Countingstuff

Reputation: 783

The dumb eval solution I had in mind, if it's what you wanted it can be made neat... 

function toMulti(arr) {
    let str = "[";
    let level = 1;
    const charLevels = { a: 1, b: 2, c: 3 };
    arr.forEach(char => {
        const charLevel = charLevels[char];
        if (level < charLevel) {
            for (let i = 0; i < charLevel - level; i++) {
                str += "[";
            }
        }
        if (level > charLevel) {
            for (let i = 0; i < level - charLevel; i++) {
                str += "],";
            }
        }
        level = charLevel;
        str += `'${char}',`;
    });
    for (let i = 0; i < level; i++) {
        str += "]";
    }
    return eval(str);
}

Upvotes: 3

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