Build a tree from a flat array

user_15611520 0
Viewed 78

I was faced with the question of building a tree from a flat array. We have an array.

[
    {
        "h1": "h001",
        "h2": "z001"
    },
    {
        "h1": "h002",
        "h2": "z002"
    },
    {
        "h1": "h003",
        "h2": "z003"
    }
]

I would like to get something like this:

[{
    "h1": "h001",
    "h2": "z001",
    "children": {
        "h1": "h002",
        "h2": "z002",
        "children": {
            "h1": "h003",
            "h2": "z003"
        }
    }
}]

Is there a way to implement this?

Thanks!

tree nodes arrays javascript
3 Answers

This would be a great place to use the array map() method. Essentially, we'll takin a shallow copy of the array using slice(), then reverse() it, then make each object a property of the previous object's under the children property. When we are done, we re-reverse() the array to get the original order and take the first item.

let values = [{
    "h1": "h001",
    "h2": "z001"
}, {
    "h1": "h002",
    "h2": "z002"
}, {
    "h1": "h003",
    "h2": "z003"
}];

let newValues = values.slice().reverse().map((e,i,a) => i ? (a[i] = { ...e, children: a[i-1] }) : a[i]).reverse()[0];

console.log(newValues);

This outputs:

{
  "h1": "h001",
  "h2": "z001",
  "children": {
    "h1": "h002",
    "h2": "z002",
    "children": {
      "h1": "h003",
      "h2": "z003"
    }
  }
}
user_38242490

Iterate by there index and add next node to the previous index.

Implementation:

const nodes = [{ "h1": "h001", "h2": "z001" }, { "h1": "h002", "h2": "z002" }, { "h1": "h003", "h2": "z003" }];

for (let i = 1; i < nodes.length; i++) {
    nodes[i - 1].children = nodes[i];
}

console.log('solutionByIndex', nodes[0]);

user_127503990

You can use recursion:

function to_tree(vals){
   var v = vals.shift()
   return vals.length ? {...v, children:to_tree(vals)} : v
}
var vals = [{ "h1": "h001", "h2": "z001" }, { "h1": "h002", "h2": "z002" }, { "h1": "h003", "h2": "z003" }];
console.log([to_tree(vals)])

user_73267380
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