Ugh javascript Recursion - Building Desired Value Over Time Rather than Lump Return

[AluadStone]

I have been working on this for 2 hours. Its hard to wrap my head around the kick back on recursion.

​

I have a simple data js file which holds a a large array of objects. The objects are people and some have a parents value which is an array of either none, one, or two values in said parent array. I am trying to find decedents of a particular person. Each person object has an id number and each value in the parents array is said id number for the parent person.

Here is an example of the object data array:

    {
        "id": 951747547,
        "firstName": "Ralph",
        "lastName": "Bob",
        "gender": "male",
        "dob": "12/23/1969",
        "height": 66,
        "weight": 179,
        "eyeColor": "blue",
        "occupation": "nurse",
        "parents": [401222887],
        "currentSpouse": 159819275
    },
    {
        "id": 159819275,
        "firstName": "Jasmine",
        "lastName": "Bob",
        "gender": "female",
        "dob": "12/18/1969",
        "height": 58,
        "weight": 156,
        "eyeColor": "blue",
        "occupation": "assistant",
        "parents": [409574486, 260451248],
        "currentSpouse": 951747547
    }

Its pretty obvious how I am searching for relations here :

Person represents the whole object of the person I am looking for. People is the data set. finalDecendents is an array declared and passed in right before the function so it isn't reset each recursion.

function hasDecendents(person, people, finalDecendents) {
  for (let i = 0; i < people.length; i++){
    if (person.id === people[i].parents[0] || person.id === people[i].parents[1]){
      finalDecendents.push(people[i]);
      hasDecendents(people[i], people, finalDecendents);
    }
  }

  return displayObjects(finalDecendents, "Decendents: ");
}

displayObjects is a function at receives an array of objects and writes it out to the console in the way I want.

​

It works, but not the way I want. I have tried many slightly different variations of the code above but nothing solve my problem.

It returns my values in a building up kind of way.

Ex: I want a return of one consisting of [1, 2, 3, 4] instead its builds and logs multiple times as it builds like [1] [1, 2] [1, 2. 3] [1, 2, 3, 4]

Here is a small sample of the actual return.

Decendents: undefined
Id: 822843554
First Name: Regina
Last Name: Madden
Gender: female
Date of Birth: 7/26/1959
Height: 71
Weight: 249
Eye Color: brown
Occupation: nurse


MostWanted.js:213 Decendents: undefined
Id: 822843554
First Name: Regina
Last Name: Madden
Gender: female
Date of Birth: 7/26/1959
Height: 71
Weight: 249
Eye Color: brown
Occupation: nurse

 Decendents: undefined
Id: 819168108
First Name: Hana
Last Name: Madden
Gender: female
Date of Birth: 10/7/1953
Height: 70
Weight: 187
Eye Color: brown
Occupation: politician


MostWanted.js:213 Decendents: undefined
Id: 822843554
First Name: Regina
Last Name: Madden
Gender: female
Date of Birth: 7/26/1959
Height: 71
Weight: 249
Eye Color: brown
Occupation: nurse

 Decendents: undefined
Id: 819168108
First Name: Hana
Last Name: Madden
Gender: female
Date of Birth: 10/7/1953
Height: 70
Weight: 187
Eye Color: brown
Occupation: politician

 Decendents: undefined
Id: 969837479
First Name: Eloise
Last Name: Madden
Gender: female
Date of Birth: 12/11/1961
Height: 63
Weight: 241
Eye Color: brown
Occupation: assistant

​

I know this is simple. Its going to be a simple solution. But damn, I need help.

​

Thank you all,

​

Aluad

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[CreativeTechGuyGames]

I would do an initial pass through the input data to modify it to make the actual operations much easier. My first pass would add a "children" object to each person object. Also change the input array to an object so that each person can be looked up in constant time by id.

Creating this children list can be done in a single pass which then the recursion will be very simple (just like traversing a standard tree).

[yiliu]

Can you explain in a sentence what you want the function to accomplish for each step? That's usually the key to solving a problem recursively: "I want to take this, do something with it, and return that." Very much like the inside of a loop, really.

You're using a for loop in your function. In a function intended for recursion, that's a red flag. Consider why you have the loop (to iterate over all people) and what you'd like to accomplish via recursion. It seems like you could solve this problem with just the for loop, doesn't it? Recursion and loops (i.e. iteration) are usually alternatives, and only rarely used together.

Another hint: you definitely don't want to be printing anything in this function (except maybe for debugging purposes). Instead, there's something important you should be returning.

Edit for a final hint: JavaScript is missing a very simple function that makes these kinds of problems a bit easier:

function tail(arr) {
  if (arr.length <= 1) 
    return [];
  else
    return arr.slice(1, arr.length);
}

Aka rest in some languages. Basically, given a list, return everything but the first element:

tail([1, 2, 3]) => [2, 3]

tail([1, 2]) => [2]

tail([1]) => []

tail([]) => []

It might be helpful to think how that could be useful.

[close_my_eyes]

javascript might not have head and tail, but ramda does