Recursive function returning empty arrray

Question

I am having issue with my recursive function getPath, as it is returning an empty array, when it should be returning an array that looks something like this:

['main', 'children', 'name']

I am not sure if the logic pare is right, as that isn't what the question is about, the question is, why is my array empty? It is pushing data onto the array, but the final result is an empty array.

let dataScope = [{
  "name": "main",
  "location": [":data"]
}, {
  "name": "child",
  "location": ["main", "children"]
}]

function getLocation(key) {
  let val = dataScope.find(i => i.name == key)
  return val ? val.location : []
}

function getPath(items) {
  let path = []
  let item = items.shift()
  if (item) {
    let loc = getLocation(item)
    if (loc.length > 0 && loc.join('.') != ':data') {
      path.push(...getPath(loc))
      console.log('added to array')
    }
  }
  return path
}

console.log(getPath(['child', 'name']))

well, your first item fails the test, therefore you never recurse — Jaromanda X
– Jaromanda X, Commented Mar 9, 2018 at 2:49
Why not put a console.log(path) before your added to array loc then? — Mark C.
– Mark C., Commented Mar 9, 2018 at 2:52
@JaromandaX, the first item checked is child, which should not fail — smac89
– smac89, Commented Mar 9, 2018 at 2:52

Jaromanda X · Accepted Answer · 2018-03-09 03:19:08Z

1

You don't do anything with loc so, it seems nothing gets pushed to the array

Note: I'm still trying to get to grips with why your original code results in an empty array - however, this code produces the expected result :p

let dataScope = [{
  "name": "main",
  "location": [":data"]
}, {
  "name": "child",
  "location": ["main", "children"]
}]

function getLocation(key) {
  let val = dataScope.find(i => i.name == key);
  return val ? val.location : []
}

function getPath(items, indent = 0) {
  let z = items.join(',');
  console.log(`${' '.repeat(indent)}called with ${z}`);
  let path = [];
  let item = items.shift();
  let loc = [];
  if (item) {
    loc = getLocation(item);
    if (loc.length > 0 && loc.join('.') != ':data') {
      path.push(...getPath(loc.slice(), indent + 4)); // .slice() so loc isn't mutated
      console.log(`${' '.repeat(indent)}${z} has path [${path.join(',')}]`);
    }
    path.push(...loc); // add loc to the path - comment this out to see the difference
  }
  console.log(`${' '.repeat(indent)}${z} returns [${path.join(',')}]`);
  return path
}

console.log(`[${getPath(['child', 'name'])}]`)

edited Mar 9, 2018 at 3:19

answered Mar 9, 2018 at 3:10

Jaromanda X

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5 Comments

Get Off My Lawn Over a year ago

I changed yours a little by just pushing loc to the array then calling getPath(loc) afterwards without pushing that to the array, and that seems to work.

Jaromanda X Over a year ago

why?? doesn't that produce a different result order? (I don't really know what you changed though)

Get Off My Lawn Over a year ago

I changed path.push(...getPath(loc)) to path.push(...loc);getPath(loc)

Jaromanda X Over a year ago

won't that result in [main,children,:data] - not what you expected, right?

Get Off My Lawn Over a year ago

It seems to work when I do that. I also need to push what is left of the items array to the end of the path[], which I did after the if, and I am now getting [main,children,name], which looks closer to what I want for the final result. (now that I can visualize the output :))

webnetweaver · Accepted Answer · 2018-03-09 03:26:29Z

0

First youre passing an array of names to getPath but then later youre passing the location array. Which one should it be? Logic needs tweaking. And also there's nothing in the dataset using the value "name" so your test is incorrect as well.

answered Mar 9, 2018 at 3:26

webnetweaver

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Comments

guijob · Accepted Answer · 2018-03-09 03:42:26Z

Its because you're doing recursion sending dataScope location but you implemented getPath expecting dataScope keys:

let dataScope = [{
  "name": "main",
  "location": [":data"]
}, {
  "name": "child",
  "location": ["main", "children"]
}]

function getLocation(key) {
  let val = dataScope.find(i => i.name == key)
  return val ? val.location : []
}

function getPath(keys) { // changing items name to keys for clarification
  let path = []
  let key = keys.shift()
  if (key) {
    let loc = getLocation(key);
    if (loc.length > 0 && loc.join('.') != ':data') {
      path.push(...loc) // push locs into array
      getPath(keys) // call getPath with remaining keys
      console.log('added to array')
    }
  }
  return path
}

console.log(getPath(['child', 'main']))

You will not have :data into your path result because of this statement: loc.join('.') != ':data'. If you remove it you will get your expected output.

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