Convert flat array to tree structure

Question

I have a flat array that I'm getting from a MySQL query but I need to convert it into a tree structure. I've been trying to do this for a while now but can't seem to get it done.

It's basically for navigation in a web app. Some nodes will have children but others will not.

I've tried using ES6 array functions like reduce, map, etc but I can't get the child elements to show up.

Here's the structure...

[
  {
    "page_id": 1,
    "page_name": "dashboard",
    "path": "/",
    "page_icon": "dashboard",
    "sub_page_id": 0,
    "sub_page_name": null,
    "sub_page_path": null,
    "sub_page_icon": null,
    "parent_id": 0
  },
  {
    "page_id": 2,
    "page_name": "Transactions",
    "path": "/transactions",
    "page_icon": "swap_horiz",
    "sub_page_id": 0,
    "sub_page_name": null,
    "sub_page_path": null,
    "sub_page_icon": null,
    "parent_id": 0
  },
  {
    "page_id": 6,
    "page_name": "Reports",
    "path": null,
    "page_icon": null,
    "sub_page_id": 1,
    "sub_page_name": "Transactions Value",
    "sub_page_path": "/transactions-value",
    "sub_page_icon": "assessment",
    "parent_id": 6
  },
  {
    "page_id": 6,
    "page_name": "Reports",
    "path": null,
    "page_icon": null,
    "sub_page_id": 2,
    "sub_page_name": "Transactions Volume",
    "sub_page_path": "/transactions-volume",
    "sub_page_icon": "assessment",
    "parent_id": 6
  },
  {
    "page_id": 6,
    "page_name": "Reports",
    "path": null,
    "page_icon": null,
    "sub_page_id": 3,
    "sub_page_name": "Transactions Frequency",
    "sub_page_path": "/transactions-frequency",
    "sub_page_icon": "assessment",
    "parent_id": 6
  },
  {
    "page_id": 8,
    "page_name": "Holidays",
    "path": null,
    "page_icon": null,
    "sub_page_id": 7,
    "sub_page_name": "My Holidays",
    "sub_page_path": "/my-holidays",
    "sub_page_icon": "wb_sunny",
    "parent_id": 8
  },
  {
    "page_id": 8,
    "page_name": "Holidays",
    "path": null,
    "page_icon": null,
    "sub_page_id": 8,
    "sub_page_name": "Add User",
    "sub_page_path": "/add-user",
    "sub_page_icon": "person_add",
    "parent_id": 8
  },
  {
    "page_id": 8,
    "page_name": "Holidays",
    "path": null,
    "page_icon": null,
    "sub_page_id": 9,
    "sub_page_name": "Add Site",
    "sub_page_path": "/add-site",
    "sub_page_icon": "location_on",
    "parent_id": 8
  },
  {
    "page_id": 10,
    "page_name": "Logout",
    "path": "/logout",
    "page_icon": "input",
    "sub_page_id": 0,
    "sub_page_name": null,
    "sub_page_path": null,
    "sub_page_icon": null,
    "parent_id": 0
  }
]

Answer 1

Just off the top of my head, you could use a reduce .

myArray.reduce((acc, curr) => {
  if (!curr.sub_page_id)
    acc[curr.page_id] = curr
  else
    acc[curr.page_id].children = acc[curr.page_id].children
      ? acc[curr.page_id].children[curr.sub_page_id] = curr
      : acc[curr.page_id].children = { [sub_page_id]: curr }
  return acc
}, {})

Answer 2

I've done it guys. May not be the most efficient method but it works.

const data = response.data;
const tree = [];

data.reduce(function(a, b, i, r) {

    // Add the parent nodes
    if(a.page_id != b.page_id){
        tree.push({ page_id: a.page_id,
                        page_name: a.page_name,
                        page_path: a.path,
                        page_icon: a.page_icon
                    });
    }

    // Add the last parent node
    if(i+1 == data.length) {
        tree.push({ page_id: b.page_id,
                        page_name: b.page_name,
                        page_path: b.path,
                        page_icon: b.page_icon
                    });

        // Add the child nodes to the parent nodes
        data.reduce(function(a, b) {
            if(a.sub_page_id) {
                const find = tree.findIndex(f => f.page_id == a.parent_id);

                // Add the first child node to parent
                if(!("children" in tree[find])) {
                    tree[find].children = [];

                    tree[find].children.push({ page_id: a.sub_page_id,
                                                page_name: a.sub_page_name,
                                                page_path: a.sub_page_path,
                                                page_icon: a.sub_page_icon
                    });
                }
                // Add the remaining child nodes to parent nodes
                else {
                    tree[find].children.push({ page_id: a.sub_page_id,
                                                page_name: a.sub_page_name,
                                                page_path: a.sub_page_path,
                                                page_icon: a.sub_page_icon
                    });
                }
            }
            return b;
        });
    }
    return b;
});