Recursive removal of arrays inside javascript object

Question

I have the following object:

{ name: ["Jimmy","Jill"], age: [23, 42], location: { city: ["LA", "NYC"] }

For every object key there is an array value with 2 entries (always). What I'm trying to do is to recreate the object by plucking the 2nd item in the arrays. But I want this to happen recursively. So the output would be:

{ name: "Jill", age: 42, location: { city: "NYC" }

I have tried iterating through the object using Object.keys() but this doesn't appear to give me nested keys. I was wondering if there was a more elegant way to tackle this?

Many thanks in advance.

Why isn't location an array like this [{city: 'LA'}, {city: 'NY'}]? How do fields nested deeper than 1 level work? — SimpleJ
– SimpleJ, Commented Mar 15, 2018 at 0:14

Kevin Qian · Accepted Answer · 2018-03-15 00:26:38Z

1

Is this considered okay? This only works if we assume every prop would either be an Array of a plain Object.

let o = { name: ["Jimmy","Jill"], age: [23, 42], location: { city: ["LA", "NY"] }}

function rec(obj) {
    for (let key in obj) {
        if (obj[key] instanceof Array) {
            obj[key] = obj[key][1]
        } else {
            obj[key] = rec(obj[key])
        }
    }
    return obj
}

rec(o)
console.dir(o)

Or even this? (allows existence of array that contains objects and plain primitive entries)

let o = {
    primitive: 10,
    name: ["Jimmy","Jill"],
    age: [23, 42],
    location: {
        city: ["LA", "NY"],
        test: [
            {prop1: ['1', '2']},
            {prop2: ['A', 'B']}
        ]
    }
}

function rec(obj) {
    if (obj instanceof Array) {
        return rec(obj[1])
    } else if (obj instanceof Object) {
        for (let key in obj) {
            obj[key] = rec(obj[key])
        }
        return obj
    } else {
        return obj
    }
}

rec(o)
console.dir(o)

edited Mar 15, 2018 at 0:26

answered Mar 15, 2018 at 0:14

Kevin Qian

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3 Comments

GivP Over a year ago

This is beautiful. Thank you!

GivP Over a year ago

Also for anyone else seeing this, I was looking for the 2nd item in the arrays so rec(obj[1]) does the trick.

Kevin Qian Over a year ago

@GivP Yeah I totally ignored that. Fixed.

Slai · Accepted Answer · 2018-03-15 01:22:29Z

1

Might be easier to filter during parsing:

j = '{ "name": ["Jimmy","Jill"], "age": [23, 42], "location": { "city": ["LA", "NYC"] }}'

o = JSON.parse(j, (k, v) => v.constructor === Array ? v.pop() : v)

console.log( o )

answered Mar 15, 2018 at 1:22

Slai

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1 Comment

GivP Over a year ago

Lovely and elegant!

sellmeadog · Accepted Answer · 2018-03-15 00:46:15Z

0

Late to the party, but here's a "functional" option to consider. Would need to be modified to accommodate any edge cases.

const reducer = input =>
  Object.entries(input).reduce(
    (acc, [key, value]) =>
      value instanceof Array ? { ...acc, ...{ [key]: value[1] } } : { ...acc, ...reducer(value) },
    {}
  );

const input = { name: ["Jimmy", "Jill"], age: [23, 42], location: { city: ["LA", "NYC"] } };
const reduced = reducer(input);

console.log(reduced); // Output: { name: 'Jill', age: 42, city: 'NYC' }

answered Mar 15, 2018 at 0:46

sellmeadog

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