Javascript create array of unknown dimensional size

Question

Though I am programming Javascript several years and at least thought to know the most of it's features and problems, I came across a new one today.

I have an array of device, each device contains a path property. In this path property is also an array.

[
    { // Device object
        path: [1]
        name: "Device 1",...
    },
    { // Device object
        path: [1,3]
        name: "Device 13",...
    },
    { // Device object
        path: [1,3,1]
        name: "Device 131",...
    }...
]

This path property represents the path in an array, I have to create. So the structure above should result in the following (I know it is not valid JS):

[
1 => {
    name: "Device 1",
    children: [
        3 => {
            name: "Device 13",
            children: [
                1 => {
                    name: "Device 131",
                    children: [],...
                },
            ],...
        },
    ],...
},
]

In any other language like e.g. php I would use a reference or a pointer and then looping through the path-array:

$newArr = [];
$ptr = &$newArr;
foreach($path as $key){
    $ptr = &$ptr[$key].children;
}

The only way I can think of doing something like this in JS is by using eval. But maybe you got some better ideas.

To clarify what I want: The first structure should be somehow processed and be "converted to the second structure". The third and last code snippet is the approach I would use in PHP.

Thank You

Luca

Can you clarify what exactly you want to do? Do you want to create second structure from first one? — guleria
– guleria, Commented Aug 3, 2016 at 9:26
Are you trying to create such an array/object, or access data in one, or both? — qxz
– qxz, Commented Aug 3, 2016 at 9:27
I tried to clarify it in the post: The first structure should be somehow processed and be "converted to the second structure". The third and last code snippet is the approach I would use in PHP. — lal12
– lal12, Commented Aug 3, 2016 at 9:30

Marcus · Accepted Answer · 2016-08-03 09:31:18Z

1

lets try this (untested):

var tree = new Object();

for(var key in yourFlatArray){
    var path = yourFlatArray[key].path;
    var node = tree;
    while(path.length){
        if(!(path[0] in node)){
            node[path[0]] = new Object();
            node[path[0]]['children'] = new Array();
            node[path[0]]['name'] = yourFlatArray[key].name;
        }
        node = node[path[0]].children;
        path.shift();
    }
}

answered Aug 3, 2016 at 9:31

Marcus

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3 Comments

lal12 Over a year ago

Ok thank you, I actually tried that. Don't know why that didn't work, but I rewrote it and now it is working.

Marcus Over a year ago

Glad to help you :) Could you post the working version please.

pishpish Over a year ago

If you used an object to represent the tree, I think you should do the same with the children array. Also, shifting will destroy the original paths.

pishpish · Accepted Answer · 2016-08-03 10:17:29Z

You can use reduce by passing the current nested level of results object and the id (property key) of the path. Whenever a device entry does not exist, it is added to the current object.

var result = {};
devices.forEach(function(device){

    device.path.reduce(function(obj, id){
        if( !obj.hasOwnProperty(id) )
            obj[id] = { name: device.name, children: {} };
        return obj[id].children;
    }, result);

});

var devices = [{
  path: [1],
  name: "Device 1"
},{
  path: [1, 2],
  name: "Device 12"
},{
  path: [1, 3],
  name: "Device 13"
},{
  path: [1, 3, 1],
  name: "Device 131"
}];


var result = {};
devices.forEach(function(device) {

  device.path.reduce(function(obj, id) {
    if (!obj.hasOwnProperty(id))
      obj[id] = {
        name: device.name,
        children: {}
      };
    return obj[id].children;
  }, result);

});
console.log(result);

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