Question 191207 in Javascript Question posted in
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Javascript – Array conversion manipulation and formatting

I have the following array:

[
    {
        "level": "level3",
        "category": "car"
    },
    {
        "level": "level1",
        "category": "bike"
    },
    {
        "level": "level2",
        "category": "car"
    },
    {
        "level": "level5",
        "category": "bike"
    }
]

I need to convert this to the following object:

newObj = {
     car: ['level3', 'level2'],
     bike: ['level5', 'level1'],
  };

What would be the best way to achieve this? Thanks in advance

Tags:

3

Answers


  1. 0

    You could achieve what you want with many approaches:

    for...of approach

    const data = [ { "level": "level3", "category": "car" }, { "level": "level1", "category": "bike" }, { "level": "level2", "category": "car" }, { "level": "level5", "category": "bike" } ];
const newObj = {};
for (const item of data) {
  const {level,category} = item;
  if (newObj[category]) {
    newObj[category].push(level);
  } else {
    newObj[category] = [level];
  }
}
console.log(newObj);

    reduce approach

    const data = [ { "level": "level3", "category": "car" }, { "level": "level1", "category": "bike" }, { "level": "level2", "category": "car" }, { "level": "level5", "category": "bike" } ];
const newObj = data.reduce((acc, item) => {
    const { level, category } = item;
    acc[category] = acc[category] || [];
    acc[category].push(level);
    return acc;
}, {});
console.log(newObj);

    The first approach is simple and understandable and the second is a more functional approach. But both approaches have a linear time complexity of O(n), choosing one of them is just a matter of personal preference and coding style.

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  2. 0

    By using the function Array.prototype.reduce

    const array = [{        "level": "level3",        "category": "car"    },    { "level": "level1",        "category": "bike"    },    {        "level": "level2",        "category": "car"    },    {      "level": "level5",        "category": "bike"    }],
      result = array.reduce((a, {level, category}) => {
        (a[category] = a[category] || []).push(level);
        return a;
      }, {});

console.log(result);
    .as-console-wrapper { max-height: 100% !important; top: 0; }
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  3. 0

    An old-school imperative approach with a linear runtime (that is double the size of your array, and you double the time it takes for the algorithm to finish)

    const origs = [
    {
        "level": "level3",
        "category": "car"
    },
    {
        "level": "level1",
        "category": "bike"
    },
    {
        "level": "level2",
        "category": "car"
    },
    {
        "level": "level5",
        "category": "bike"
    }
]

const newObj = {}
    
for (orig of origs) {
  if (orig.category && orig.level) {
    newObj[orig.category] = newObj[orig.category] ? newObj[orig.category].concat(orig.level) : [orig.level]
  }  
}

    Also, it’s a good idea to watch for the presence of the fields category
    and level.

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