count 'last children' from any point in javascript object/array structure

Question

I've got a data set simplified to the following

var data = {
  foo: 'bar'
  children: [
    {
      foo: 'bar'
      children: [ 
        { foo: 'bar' }, // count
        { foo: 'bar' }, // count
        {
          foo: 'bar'
          children: [
            { foo: 'bar' }, // count
            { foo: 'bar' }, // count
          ]
        },
        { foo: 'bar' }, // count
      ]
    },
    {
      // etc
    }
  ]
}

There's a lot more of it than that. Any number of objects below nested.

{
  foo: 'bar'
  children: []
}

I want to be able to calculate the total 'last children' of any 'node' in the structure. So far I have written a quick script that will work it out from the top level using a counter variable scoped outside of the recursing function - but that stop it being re-usable.

var total = 0;

var countLastChildren = function(object) {

  if(object.children) {
    object.children.forEach(function(el){
      countLastChildren(el);
    }); 
  } else {
    total++;
  }
}
countLastChildren(data);
console.log(total);

I can't quite get my head round how to scope the counter inside countLastChildren() to allow it to return a value and make it re-usable by passing in different objects or objects nested within my main structure.

Any ideas? Thanks

If data is the structure shown, what would be the desired result from countLastChildren(data)? 7 (all the children of the top-most level), or 2 (just the lowest level children), or...? — nnnnnn
– nnnnnn, Commented Aug 14, 2013 at 11:31
I've added some comments to show where I'd like to 'count'. It's basically count all objects without children. — joevallender
– joevallender, Commented Aug 14, 2013 at 11:34

arghbleargh · Accepted Answer · 2013-08-14 11:33:17Z

4

You can just have the function return the count:

var countLastChildren = function(object) {

    if(object.children) {
        var return_val = 0;
        object.children.forEach(function(el){
            return_val += countLastChildren(el);
        });
        return return_val; 
    } else {
        return 1;
    }
}
console.log(countLastChildren(data));

answered Aug 14, 2013 at 11:33

arghbleargh

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2 Comments

joevallender Over a year ago

Ah that's right, I thought I was missing something simple. It's hard to visualise recursion (particularly including return values) sometimes

joevallender Over a year ago

Marking this one as accepted since it points out a good change in my original code :) Probly easiest to follow for a googler too

Sacho · Accepted Answer · 2013-08-14 11:43:24Z

2

Some code golf:

function Total(obj) {
      return obj.children 
      ? obj.children.map(Total).reduce(function (prev, cur) { return prev + cur; }) 
      : 1;
}

answered Aug 14, 2013 at 11:43

Sacho

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1 Comment

joevallender Over a year ago

really like that. in fact really like any use of map/reduce :-) can confirm that works on my full set of data. Would need underscore or something if used in the browser though

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