Reduce array of object properties to nested object

Question

I have an array with increasing specificity eg.

const locationProperties = ['earth', 'americas', 'canada', 'saskatchewan'];

and I would like an object:

{
 earth: {
  americas: {
   canada: {
    saskatchewan: {
      // data 
    }
   }  
  }
 }
}

I was thinking to use .reduce to create the object but after applying the transformation in the reducer I am only left with {}

const reducer = (accumulator, item) => {
  accumulator[item] = {};
  return accumulator[item];
}

const reducedArray = locationProperties.reduce(reducer, {});

Mulan · Accepted Answer · 2021-03-05 00:05:38Z

4

I would recommend a simple recursion function, nest -

const nest = ([key, ...more], val) =>
  key == null
    ? val
    : {[key]: nest(more, val)}
    
const loc =
  ['earth', 'americas', 'canada', 'saskatchewan']    

console.log(nest(loc, "something"))

{
  "earth": {
    "americas": {
      "canada": {
        "saskatchewan": "something"
      }
    }
  }
}

You can also use reduceRight -

const loc =
  ['earth', 'americas', 'canada', 'saskatchewan']    

const result =
  loc.reduceRight((val, key) => ({[key]: val}), "something")

console.log(result)

{
  "earth": {
    "americas": {
      "canada": {
        "saskatchewan": "something"
      }
    }
  }
}

Since you are familiar with reduce I will point out that arr.reduceRight(...) is the effectively the equivalent of arr.reverse().reduce(...). However using reduceRight is more efficient in this case and will not mutate the input array -

const loc =
  ['earth', 'americas', 'canada', 'saskatchewan']    

const result =
  loc.reverse().reduce((val, key) => ({[key]: val}), "something")

console.log(result)

{
  "earth": {
    "americas": {
      "canada": {
        "saskatchewan": "something"
      }
    }
  }
}

edited Mar 5, 2021 at 0:05

answered Mar 4, 2021 at 23:59

Mulan

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3 Comments

Miu Over a year ago

Wow. This is beautiful. I like this solution a lot. I also tried to solve this question, but mine isn't as beautiful as yours. I think it will be more perfect if you change the argument "something" to {}?

Mulan Over a year ago

Thanks for the comment, Miu. I really appreciate it. I made the inner var "something" to signal that it can be whatever the caller wants. Also I didn't want people to get confused thinking {} was the beginning of the outermost object.

Miu Over a year ago

I got it :) Thank you for your kind reply. Now I fully agree with you and "something" :)

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