javascript - Grouping a nested array with underscore.js -

sorry if seems duplicate, i've tried other answers , can't seem works properly. i'm building angularjs spa, , have data in following format:

"folders": [   {     "id": 1,     "password": "wpaugor452",     "year": 2013   },   {             "id": 2,     "password": "wpaugor452",     "year": 2013   },   {             "id": 3,     "password": "dfgoerj305",     "year": 2014   } 

and many many more.

i want folders grouped it's this:

"folders": [   "2013": [     "wpaugor452": [       {         "id": 1,         "password": wpaugor452,         "year": 2013,       },       {         "id": 2,         "password": wpaugor452,         "year": 2013,       }                  ]   ],   "2014": [     "dfgoerj305": [       {                 "id": 3,         "password": "dfgoerj305",         "year": 2014       }     ]   ] ] 

there lot more real data, i've stripped down want group by. @ present, every folder has password , year, , want them grouped password within years, can display year in ui, , folders appropriate specific password.

although please note i'll want display year , password in ui (only once, grouped items below!)

if further detail needed, please ask.

this should want:

var result = _.chain(folders)     .groupby('year')     .mapobject( year => _.groupby(year, 'password'))     .value(); 

and version full function definition:

var result = _.chain(folders)     .groupby('year')     .mapobject(function(year) {         return _.groupby(year, 'password');     })     .value(); 

the solution first groups year , groups password each year group.