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up vote 14 down vote favorite
6

I'm trying to iterate through a nested object to retrieve a specific object identified by a string. In the sample object below, the identifier string is the "label" property. I can't wrap my head around how to iterate down through the tree to return the appropriate object. Any help or suggestions would be greatly appreciated.

var cars = 
    {
        label: 'Autos',
        subs:
            [
                {
                    label: 'SUVs',
                    subs: []
                },
                {
                    label: 'Trucks',
                    subs: [
                              {
                                label: '2 Wheel Drive',
                                subs: []
                              },
                              {
                                label: '4 Wheel Drive',
                                subs: [
                                          {
                                            label: 'Ford',                                        
                                            subs: []
                                          },
                                          {
                                            label: 'Chevrolet',
                                            subs: []                                      
                                          }
                                      ]                          
                              }
                          ]    
                },
                {
                    label: 'Sedan',
                    subs: []
                }
            ]
    }
share|improve this question
1  
possible duplicate of Traverse all the Nodes of a JSON Object Tree with JavaScript – Diodeus Nov 10 '11 at 19:15
    
You're wanting to search through all levels of the object for an arbitrary label? (Aha, traverse, that was the word I was looking for.) – Dave Nov 10 '11 at 19:16
    
Possible duplicate of Access / process (nested) objects, arrays or JSON – Liam Oct 20 at 15:29
up vote 22 down vote accepted

You can create a recursive function like this to do a depth-first traversal of the cars object.

var findObjectByLabel = function(obj, label) {
    if(obj.label === label) { return obj; }
    for(var i in obj) {
        if(obj.hasOwnProperty(i)){
            var foundLabel = findObjectByLabel(obj[i], label);
            if(foundLabel) { return foundLabel; }
        }
    }
    return null;
};

which can be called like so

findObjectByLabel(car, "Chevrolet");
share|improve this answer
    
In the original post, the sub-cars are not properties of the car object, but are contained in a subs array. – James Clark Nov 10 '11 at 19:35
    
@JamesClark I know. It should still work, and it is flexible in case he has more than one array property of if he decides to change the name of subs to something else. – Peter Olson Nov 10 '11 at 19:37
1  
Recursion is bad for very deep objects. You will get stack overflow. – Arjun U. Feb 9 '15 at 11:33
    
@ArjunU. It's fairly uncommon to have objects that are hundreds of levels deep. – Peter Olson Feb 9 '15 at 18:53
1  
@Vishal Without the obj.hasOwnProperty(i), custom prototype properties will be included. For example, if you define Array.prototype.first = function(a) { return a[0] }, then for(var i in []) will include the prototype property first. – Peter Olson Oct 10 '15 at 0:50
up vote 2 down vote

The following code assumes no circular references, and assumes subs is always an array (and not null in leaf nodes):

function find(haystack, needle) {
  if (haystack.label === needle) return haystack;
  for (var i = 0; i < haystack.subs.length; i ++) {
    var result = find(haystack.subs[i], needle);
    if (result) return result;
  }
  return null;
}
share|improve this answer
up vote 2 down vote

To increase performance for further tree manipulation is good to transform tree view into line collection view, like [obj1, obj2, obj3]. You can store parent-child object relations to easy navigate to parent/child scope.

Searching element inside collection is more efficient then find element inside tree (recursion, addition dynamic function creation, closure).

share|improve this answer
up vote -6 down vote

Try something like this:

cars.subs[0].subs[0].label

if you want to actually iterate you can do a for loop on each object in a recursive function and call that recursive function every time you hit the "subs" property of that object. This can cause issue though if you have a very deep object structure

share|improve this answer
    
This works only if you know the depth already, and that depth is exactly the same everywhere. – shoover Jul 14 '15 at 22:24

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