One liner to flatten nested object

I need to flatten a nested object. Need a one liner. Not sure what the correct term for this process is. I can use pure Javascript or libraries, I particularly like underscore.

I've got ...

{
  a:2,
  b: {
    c:3
  }
}

And I want ...

{
  a:2,
  c:3
}

I've tried ...

var obj = {"fred":2,"jill":4,"obby":{"john":5}};
var resultObj = _.pick(obj, "fred")
alert(JSON.stringify(resultObj));

Which works but I also need this to work ...

var obj = {"fred":2,"jill":4,"obby":{"john":5}};
var resultObj = _.pick(obj, "john")
alert(JSON.stringify(resultObj));

Solution 1:

Here you go:

Object.assign({}, ...function _flatten(o) { return [].concat(...Object.keys(o).map(k => typeof o[k] === 'object' ? _flatten(o[k]) : ({[k]: o[k]})))}(yourObject))

Summary: recursively create an array of one-property objects, then combine them all with Object.assign.

This uses ES6 features including Object.assign or the spread operator, but it should be easy enough to rewrite not to require them.

For those who don't care about the one-line craziness and would prefer to be able to actually read it (depending on your definition of readability):

Object.assign(
  {}, 
  ...function _flatten(o) { 
    return [].concat(...Object.keys(o)
      .map(k => 
        typeof o[k] === 'object' ?
          _flatten(o[k]) : 
          ({[k]: o[k]})
      )
    );
  }(yourObject)
)

Solution 2:

Simplified readable example, no dependencies

/**
 * Flatten a multidimensional object
 *
 * For example:
 *   flattenObject{ a: 1, b: { c: 2 } }
 * Returns:
 *   { a: 1, c: 2}
 */
export const flattenObject = (obj) => {
  const flattened = {}

  Object.keys(obj).forEach((key) => {
    const value = obj[key]

    if (typeof value === 'object' && value !== null && !Array.isArray(value)) {
      Object.assign(flattened, flattenObject(value))
    } else {
      flattened[key] = value
    }
  })

  return flattened
}

Features

• No dependencies
• Works with null values
• Works with arrays
• Working example https://jsfiddle.net/webbertakken/jn613d8p/26/

Solution 3:

Here is a true, crazy one-liner that flats the nested object recursively:

const flatten = (obj, roots=[], sep='.') => Object.keys(obj).reduce((memo, prop) => Object.assign({}, memo, Object.prototype.toString.call(obj[prop]) === '[object Object]' ? flatten(obj[prop], roots.concat([prop]), sep) : {[roots.concat([prop]).join(sep)]: obj[prop]}), {})

Multiline version, explained:

// $roots keeps previous parent properties as they will be added as a prefix for each prop.
// $sep is just a preference if you want to seperate nested paths other than dot.
const flatten = (obj, roots = [], sep = '.') => Object
  // find props of given object
  .keys(obj)
  // return an object by iterating props
  .reduce((memo, prop) => Object.assign(
    // create a new object
    {},
    // include previously returned object
    memo,
    Object.prototype.toString.call(obj[prop]) === '[object Object]'
      // keep working if value is an object
      ? flatten(obj[prop], roots.concat([prop]), sep)
      // include current prop and value and prefix prop with the roots
      : {[roots.concat([prop]).join(sep)]: obj[prop]}
  ), {})

An example:

const obj = {a: 1, b: 'b', d: {dd: 'Y'}, e: {f: {g: 'g'}}}
const flat = flatten(obj)
{
  'a': 1, 
  'b': 'b', 
  'd.dd': 'Y', 
  'e.f.g': 'g'
}

Happy one-liner day!

Solution 4:

It's not quite a one liner, but here's a solution that doesn't require anything from ES6. It uses underscore's extend method, which could be swapped out for jQuery's.

function flatten(obj) {
    var flattenedObj = {};
    Object.keys(obj).forEach(function(key){
        if (typeof obj[key] === 'object') {
            $.extend(flattenedObj, flatten(obj[key]));
        } else {
            flattenedObj[key] = obj[key];
        }
    });
    return flattenedObj;    
}