algorithm - Javascript Recursion Tree Building -

i having issue building tree flat array. building category -> subcategory tree in parent has subcategories array.

here flat array like:

[   {     "id": 1   },   {     "id": 5,   },   {     "id": 2,     "parent_id": 1   },   {     "id": 3,     "parent_id": 1   },   {     "id": 42,     "parent_id": 5   },   {     "id": 67,     "parent_id": 5   } ] 

and need result look:

[   {     "id":1,     "subcategories":[       {         "id":2,         "parent_id":1       },       {         "id":3,         "parent_id":1       }     ]   },   {     "id":5,     "subcategories":[       {         "id":42,         "parent_id":5       },       {         "id":67,         "parent_id":5       }     ]   } ] 

i have tried recursively recursively searching children , attaching array , continuing until hit bottom of barrel getting cyclic structure. appears parent_id in traverse id of parent... ideas:

tree(passinginflatobjecthere);  function toplevel (data) {   let blob = [];   data.foreach((each) => {     if (!each.parent_id) {       blob.push(each);     }   });   return blob; }  function tree (data) {   let blob = toplevel(data).map(function (each) {     each.subcategories = traverse(data, each.id);     return each;   });   return blob; }  function traverse (data, parent_id) {   let blob = [];   if (!parent_id) {     return blob;   }   data.foreach((each) => {     if (each.id === parent_id) {       each.subcategories = traverse(data, each.id);       blob.push(each);     }   });   return blob; } 

i don’t want fix problem take full advantage of es6

first of toplevel function can rewritten this:

function toplevel(data) {   return data.filter(node => !node.parent_id); } 

neat isn’t it? recommend changing tree consistency that’s of course stylistic.

function tree(data) {   return toplevel(data).map(each => {     each.subcategories = traverse(data, each.id);     return each;   }); } 

no logic issues far. traverse, however, contains one, when check each.id === parent_id. this, functions searches node id parent_id. mistake. wanted each.parent_id === parent_id.

your issue solved now. stop reading if bother you. take advantage of filter here , remove superfluous exit , rewrite function to:

function traverse(data, parentid) {   const children = data.filter(each => each.parent_id === parentid);   children.foreach(child => {     child.subcategories = traverse(data, child.id);   });   return children; }