Transform flat array of objects into nested arrays according to group property

Question

I have a flat array of objects like this:

[
   { id: 0 },
   { id: 1, group: "a" },
   { id: 2, group: "a" },
   { id: 3, group: "a/b" },
   { id: 4 },
   { id: 5, group: "a/b" },
]

the goal is to transform this array into a nested array based on the group property. The expected result would look like this:

[
   { id: 0 },
   [
      { id: 1, group: "a" },
      { id: 2, group: "a" }
      [
         { id: 3, group: "a/b" },
         { id: 5, group: "a/b" }
      ],       
   ],
   { id: 4 },
]

Is there an easy way to accomplish that?

Since you actually need to parse the group content and items are not ordered, you'd need to iterate and IMHO order the elements before you do the nesting. — Laur Ivan
– Laur Ivan, Commented Oct 2, 2017 at 8:27
@NinaScholz, basically the sub-arrays should appear where the first element of that specific group was defined in the original array. Not sure if that makes any sense. Maybe I haven't thought this through enough ;) — Đinh Carabus
– Đinh Carabus, Commented Oct 2, 2017 at 8:28

Nina Scholz · Accepted Answer · 2017-10-02 08:37:26Z

2

You could use a dynamic approach with a nested hash table for nested level of items.

var data = [{ id: 0 }, { id: 1, group: "a" }, { id: 2, group: "a" }, { id: 3, group: "a/b" }, { id: 4 }, { id: 5, group: "a/b" }],
    result = [],
    hash = { _: result };

data.forEach(function (o) {
    if (!o.group) {
        hash._.push(o);
        return;
    }
    o.group.split('/').reduce(function (r, k) {
        if (!r[k]) {
            r[k] = { _: [] };
            r._.push(r[k]._);
        }
        return r[k];
    }, hash)._.push(o);
});

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Oct 2, 2017 at 8:37

Nina Scholz

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Comments

Laur Ivan · Accepted Answer · 2017-10-02 08:25:21Z

1

IMHO it's a bit convoluted. It's easier to create a dict with the key being the content of the group and use that.

If you don't have to be particularly efficient, I'd:

create a dict with the key being the content of the group.
order the keys (e.g. alphabetically)
For each key:
1. Check the previous key and see if it's an extension (e.g. 'a/b' has '/b' compared to the previous key 'a'
2. if you have an extension, then push the key on a stack and create a nesting level in your array
3. else if the key is not extending the previous key, pop until you get the an extension or top of the stack
4. add to the extension all elements from the dict you created at the first step

This should do it.

answered Oct 2, 2017 at 8:25

Laur Ivan

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1 Comment

Đinh Carabus Over a year ago

Thank you, efficiency is not the problem here. The actual arrays are really small.

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