Multi-Dimensional Array within Object

Question

Please go through this javascript object:

var obj = [{
  id: "A",
  children: [{
    id: "B",
    children: [{
      id: "C",
      children: [{
        id: "D",
        children: [{
          id: "E",
          children: [{
            id: "F"
          }]
        }]
      }, {
        id: "G",
        children: {
          id: "H"
        }
      }]
    }, {
      id: "I"
    }]
  }, {
    id: "J",
    children: [{
      id: "K"
    }]
  }]
}, {
  id: "L"
}, {
  id: "M",
  children: {
    id: "N",
    children: [{
      id: "O"
    }]
  }
}, {
  id: "P"
}];

How to write JavaScript code to recursively parse it and print all the IDs in console so that the output looks like:

A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P

This is how far I could reach. I couldn't think of any logic after that.

for ( i=0 ; i < obj.length ; i++ ){
         var objId = obj[i];
         for( j=i; j<1 ; j++){
             console.log(obj[j].id);
             console.log(obj[j].children[j].id);
         }
     }

I don't understand what logic should be applied here. Do help.

Answer 1

You could use an iterative and recursive approach with a depth-first search algorithm.

Edit: Extended for children as object.

 var data = [{ id: "A", children: [{ id: "B", children: [{ id: "C", children: [{ id: "D", children: [{ id: "E", children: [{ id: "F" }] }] }, { id: "G", children: { id: "H" } }] }, { id: "I" }] }, { id: "J", children: [{ id: "K" }] }] }, { id: "L" }, { id: "M", children: { id: "N", children: [{ id: "O" }] } }, { id: "P" }]; data.forEach(function iter(a) { console.log(a.id); if (Array.isArray(a.children)) { a.children.forEach(iter); return; } if (a.children && typeof a.children === 'object') { // omit this part iter(a.children); // if children is } // always an array }); 

This version collects all necessary data and returns it in an array.

 var data = [{ id: "A", children: [{ id: "B", children: [{ id: "C", children: [{ id: "D", children: [{ id: "E", children: [{ id: "F" }] }] }, { id: "G", children: { id: "H" } }] }, { id: "I" }] }, { id: "J", children: [{ id: "K" }] }] }, { id: "L" }, { id: "M", children: { id: "N", children: [{ id: "O" }] } }, { id: "P" }], result = data.reduce(function iter(r, o) { r.push(o.id); if (Array.isArray(o.children)) { return o.children.reduce(iter, r); } if (o.children && typeof o.children === 'object') { // omit this part return iter(r, o.children); // if children is } // always an array return r; }, []); console.log(result); 

 .as-console-wrapper { max-height: 100% !important; top: 0; } 

Answer 2

You could use the below ES6 function. Note that at two places you did not define children as an array, which I assume is a mistake. If it is indented, I would strongly advise to reconsider, and make it consistent throughout.

 function getIds(data) { return data.reduce((acc, el) => acc.concat(el.id, getIds(el.children || [])), []) } var obj = [{ id: "A", children: [{ id: "B", children: [{ id: "C", children: [{ id: "D", children: [{ id: "E", children: [{ id: "F" }] }] }, { id: "G", children: [{ id: "H" }] }] }, { id: "I" }] }, { id: "J", children: [{ id: "K" }] }] }, { id: "L" }, { id: "M", children: [{ id: "N", children: [{ id: "O" }] }] }, { id: "P" }]; console.log(getIds(obj).join('\\n')); 

 .as-console-wrapper { max-height: 100% !important; top: 0; } 

Answer 3

What you are showing looks like it is asking for a depth first solution, as the order of the ids are clearly alphabetical and they are ordered by first encountered then by depth.

As a result, every id encountered will be collected, and then the deeper ids will be examined. This can, and probably should, be done with recursion.

Here is an example.

 var obj=[{id:"A",children:[{id:"B",children:[{id:"C",children:[{id:"D",children:[{id:"E",children:[{id:"F"}]}]},{id:"G",children:{id:"H"}}]},{id:"I"}]},{id:"J",children:[{id:"K"}]}]},{id:"L"},{id:"M",children:{id:"N",children:[{id:"O"}]}},{id:"P"}]; var ids = [];//output holder (function tree(cur){ //recursive function for(var i = 0; i < cur.length; i++){ //iterate current set ids.push(cur[i].id); //always store id if(cur[i].children) tree(cur[i].children); //recurse if children exist } })(obj) //start from the top console.log(ids);