Convert multidimensional array to object

Question

I have a 2d array with up to [32][32] entries. And I'd like to convert it from something like this:

[
    null, 
    null, 
    null, 
    null, 
    null, 
    null, 
    [null, null, null, null, null, null, null, null, null, null, "player1"],
    [null, null, null, null, null, "player2"]
]

to

{
  "6": {"10":"player1"},
  "7": {"5":"player2"}
}

So this would be my array:

var gameField = [];
gameField[6] = [];
gameField[6][10] = "player1";
gameField[7] = [];
gameField[7][5] = "player2";

Now I tried to use this:

var obj = {}
obj = Object.assign({},gameField);
console.log(JSON.stringify(obj));

but it only worked for the outer array, the inner arrays were not affected:

{
    "6": [null, null, null, null, null, null, null, null, null, null, "player1"],
    "7": [null, null, null, null, null, "player2"]
}

What would be the shortest way to do this properly?

This seems like a very bad structure, before and after. Dynamic object keys are mostly hard to use. Why don't you use something cleaner like for example [ {player:'player1', numberOfX:10}, {player:'player2', numberOfX:5} ]. — str
– str, Commented Jul 25, 2016 at 12:13
The structure is a bit more complicated in reality. There is more than just players. What I want to achive is to simply convert a 2d array into an object that uses the array indexes as keys. So that I can get rid of all the null values of the array. — Forivin
– Forivin, Commented Jul 25, 2016 at 12:15
@Forivin If your structure is even more complicated, my point is even more appropriate. — str
– str, Commented Jul 25, 2016 at 12:17

Steve Greatrex · Accepted Answer · 2016-07-25 12:16:20Z

6

You can iterate over the items in the array and then recurse if the located item is itself an array (check using Array.isArray)

function populateFromArray(array) {
  var output = {};
  array.forEach(function(item, index) {
    if (!item) return;
    if (Array.isArray(item)) {
      output[index] = populateFromArray(item);
    } else {
      output[index] = item;
    }
  });
  return output;
}

console.log(populateFromArray(input));

This results in:

[object Object] {
  6: [object Object] {
    10: "player1"
  },
  7: [object Object] {
    5: "player2"
  }
}

See a working jsBin

Note: you can certainly do this in less code but less code is not always better!

answered Jul 25, 2016 at 12:16

Steve Greatrex

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3 Comments

Forivin Over a year ago

Nice, it works. Can you elaborate a bit on the "less code" thingy?

Steve Greatrex Over a year ago

If you see the answer from @redu then you have a perfect example. This is much less code but - in my opinion - is much harder to understand.

Forivin Over a year ago

The good thing about your code is that is doesn't break if you place objects instead of strings in the original array.

Redu · Accepted Answer · 2016-07-25 14:33:15Z

3

Array.prototype.reduce() seems ideal for this. You may do as follows;

var dataArr = [null,null,null,null,null,null,[null,null,null,null,null,null,null,null,null,null,"Player1"],[null,null,null,null,null,"player2"]],
    dataObj = dataArr.reduce((p,c,i) => (Array.isArray(c) && (p[i] = {[c.length-1]:c[c.length-1]}),p),{});
console.log(dataObj);

edited Jul 25, 2016 at 14:33

answered Jul 25, 2016 at 12:25

Redu

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2 Comments

Forivin Over a year ago

Though if I use an object like {id:0,name:'Player1'} instead of "player1", I cannot access the property anymore after the conversion.

Redu Over a year ago

@Forivin... Sorry there was an extra set of brackets that i overlooked which was resulting an array ["player1"] instead of a string "player1". Now it should be ok.

trincot · Accepted Answer · 2016-07-25 12:38:34Z

1

You could use this recursive function, using ES6 code:

var data = [null,null,null,null,null,null,[null,null,null,null,null,null,null,null,null,null,"player1"],[null,null,null,null,null,"player2"]];

function convert(data) {
    return Array.isArray(data)
        ? data.reduce( (obj, el, i) => (el && (obj[i] = convert(el)), obj), {} )
        : data;
}

var obj = convert(data);

console.log(obj);

This will also work when your input array is nested deeper than 2 levels. It does not require the non-null elements to be at the end of their (sub-)array, nor that there is only one non-null element per (sub-)array.

edited Jul 25, 2016 at 12:38

answered Jul 25, 2016 at 12:26

trincot

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