Convert nested array into object

Question

An API I'm talking to returns it's registry in a very odd nested array structure. I want to convert this monstrosity into an object so my application has easy access to whole objects stored within this output.

The output the API gives me looks like this:

[ 
    [ "settings", "autoLogout", "false" ], 
    [ "settings", "autoLogoutMinutes", "60" ], 
    [ "settings", "presets", "true" ], 
    [ "controller", "rs232", "ip", "192.168.1.11" ], 
    [ "controller", "rs232", "name", "NX-22" ], 
    [ "source", "M23836", "slot1", "ip", "192.168.1.30" ]
]

The last value in each array represents the value of an entry, everything before that last one adds up to the key used to save the value. Because of size limitations I can't just drop big json-encoded objects in there, so thats not a viable workaround.

I've now made a pretty dirty and slow solution involving 2 eval()'s. (I know... that's a no-no so I'm looking for a better solution) I'm guessing this can be done loads faster, but I can't figure out how...

The snippet below uses angular because my application is Angular based, but I'm open to any fast/clean solution. A vanilla js approach or some clever use of something like lodash or underscore would be very welcome.

My dirty and slow solution now

function DemoCtrl($scope){ 
	$scope.data = [ 
        [ "settings", "autoLogout", "false" ], 
        [ "settings", "autoLogoutMinutes", "60" ], 
        [ "settings", "presets", "true" ], 
        [ "controller", "rs232", "ip", "192.168.1.11" ], 
        [ "controller", "rs232", "name", "NX-22" ], 
        [ "source", "M23836", "slot1", "ip", "192.168.1.30" ]
    ]
    
    $scope.init = function(){
        var registry = {};
        
        angular.forEach($scope.data, function(entry){
            var keys = '';
            entry.forEach(function(value, key, entry){
            
                if( key != entry.length - 1 ){
                    //not last of array, so must be a key
                    keys += '[\'' + value + '\']';
                    // check if the object already exists
                    if( !angular.isDefined( eval('registry' + keys) ) ){
                        eval('registry' + keys + ' = {}'); 
                    }
                }else{ 
                	//last one in this entry, must be the value
                  	eval('registry' + keys + ' = \'' + value + '\''); 
               	}
                
            });        
        });
        
        console.log('registry final');
        console.log(registry);
        $scope.registry = registry;
    }
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>

<div ng-app>
  
  <div ng-controller="DemoCtrl" ng-init="init()">
    <pre>{{ registry | json }}</pre>
  </div>
    
</div>

Answer 1

Here's a solution that fits your need. Also, please, never use eval. There's always a better way in JavaScript.

You can adapt the code below to your use case.

var data = [ 
    [ "settings", "autoLogout", "false" ], 
    [ "settings", "autoLogoutMinutes", "60" ], 
    [ "settings", "presets", "true" ], 
    [ "controller", "rs232", "ip", "192.168.1.11" ], 
    [ "controller", "rs232", "name", "NX-22" ], 
    [ "source", "M23836", "slot1", "ip", "192.168.1.30" ]
];

var o = {};

data.forEach(function(a) {
  var keys = a.slice(0, a.length-2);
  var cur = o;

  keys.forEach(function(k) {
    if (cur[k] == null) {
      cur[k] = {};
    }
    cur = cur[k];
  });

  cur[a[a.length-2]] = a[a.length-1]
});

output.innerHTML = JSON.stringify(o, null, 2);

<pre id='output'></pre>

Answer 2

A compact solution which avoids the calculation of the value position in the array.

var array = [
        ["settings", "autoLogout", "false"],
        ["settings", "autoLogoutMinutes", "60"],
        ["settings", "presets", "true"],
        ["controller", "rs232", "ip", "192.168.1.11"],
        ["controller", "rs232", "name", "NX-22"],
        ["source", "M23836", "slot1", "ip", "192.168.1.30"]
    ],
    obj = {};

array.forEach(function (a) {
    var p = obj,
        v = a.pop(),
        k = a.reduce(function (r, b) {
            p[r] = p[r] || {};
            p = p[r];
            return b;
        });
    p[k] = v;
});

document.write('<pre>' + JSON.stringify(obj, 0, 4) + '</pre>');