Convert parent-child array to tree

Question

Can anyone help converting the following list of parent-child objects:

[
   {
      \"name\":\"root\",
      \"_id\":\"root_id\",
   },
   {
      \"name\":\"a1\"         


        

Answer 1

Borrowing the caching logic from Vivin Paliath's answer, I have created a reusable function to convert a list of data with child-parent relationships into a tree.

var data = [
  { "id" : "root"                     },
  { "id" : "a1",   "parentId" : "root", },
  { "id" : "a2",   "parentId" : "a1",   },
  { "id" : "a3",   "parentId" : "a2",   },
  { "id" : "b1",   "parentId" : "root", },
  { "id" : "b2",   "parentId" : "b1",   },
  { "id" : "b3",   "parentId" : "b1",   }
];
var options = {
  childKey  : 'id',
  parentKey : 'parentId'
};
var tree = walkTree(listToTree(data, options), pruneChildren);

document.body.innerHTML = '
' + JSON.stringify(tree, null, 4) + '
';

function listToTree(list, options) {
  options = options || {};
  var childKey    = options.childKey    || 'child';
  var parentKey   = options.parentKey   || 'parent';
  var childrenKey = options.childrenKey || 'children';
  var nodeFn      = options.nodeFn      || function(node, name, children) {
    return { name : name, children : children };
  };
  var nodeCache = {};
  return list.reduce(function(tree, node) {
    node[childrenKey] = [];
    nodeCache[node[childKey]] = node;
    if (typeof node[parentKey] === 'undefined' || node[parentKey] === '') {
      tree = nodeFn(node, node[childKey], node[childrenKey]);
    } else {
      parentNode = nodeCache[node[parentKey]];
      parentNode[childrenKey].push(nodeFn(node, node[childKey], node[childrenKey]));
    }
    return tree;
  }, {});
}

function walkTree(tree, visitorFn, parent) {
  if (visitorFn == null || typeof visitorFn !== 'function') {
    return tree;
  }
  visitorFn.call(tree, tree, parent);
  if (tree.children && tree.children.length > 0) {
    tree.children.forEach(function(child) {
      walkTree(child, visitorFn, tree);
    });
  }
  return tree;
}

function pruneChildren(node, parent) {
  if (node.children.length < 1) {
    delete node.children;
  }
}