Creating recursive list of objects

Question

I want to create a function in Javascript which takes an array as argument and returns a list of objects. I have an array like this:

var arr= [10,20,30];
console.log(listFunction(arr));

The result should look like this:

{'val':10, 'restList':{'val':20, 'restList':{'val':30,'restList':'null'}}}

I have tried the forEach() function:

function listFunction(parentArr) {
    var listOfObjects = [];
    parentArr.forEach(function (entry, thisArg) {
        var singleObj = {}
        singleObj['val'] = entry;
        singleObj['restList'] = singleObj;
        listOfObjects[thisArg] = singleObj;
    });
    return listOfObjects;
};

@ryanyuyu a list of node and successor. yes like Linked-list — Ammar Hayder Khan
– Ammar Hayder Khan, Commented Mar 31, 2015 at 13:19
It would be easier if the inner most restList should be {} instead of null. — Ja͢ck
– Ja͢ck, Commented Apr 1, 2015 at 0:24

George · Accepted Answer · 2015-04-01 04:54:15Z

4

You need to use a recursive function:

function listFunction(arr){

   if(arr.length == 0){
       return null;
   }else{
       return {val: arr[0], restList: listFunction(arr.slice(1,arr.length))};
   }
 }

edited Apr 1, 2015 at 4:54

George

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answered Mar 31, 2015 at 13:19

Ansemo Abadía

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2 Comments

Ansemo Abadía Over a year ago

You can send the next position of array. But you need create another function. function listFunction(arr, index)... And you need to increase the index in each step.

Rick Hitchcock Over a year ago

Quick note: arr.length isn't needed in the slice function. If the second parameter is missing, it defaults to the length of the array.

ryanyuyu · Accepted Answer · 2015-03-31 13:35:32Z

This is the Lisp-style recursive list algorithm.

var recursiveList = function (array) {
  return recursiveListHelper(arr, {});
};

var recursiveListHelper = function (array, obj) {
  if (array.length === 0) //stopping condition
    return null;

  var car = array[0];       //current element
  var cdr = array.slice(1); //rest of list
  obj = {val: car};
  obj.restList = recursiveListHelper(cdr, obj);
  return obj;
};

You mentioned that you wanted to avoid using Array.slice. This solution uses array indexing instead of splitting into subarrays.

var recursiveIndexed = function (array) {
  return recursiveIndexedHelper(array, {}, 0);
};

var recursiveIndexedHelper = function (array, obj, index) {
  if (index == array.length)
    return null;

  var car = array[index];
  obj = {val: car };
  obj.restList = recursiveIndexedHelper(array, obj, index + 1);
  return obj;
};

A plunker as example.

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