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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?

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?

• javascript
• arrays
• json
• object
• multidimensional-array

Share Improve this question Follow edited Jul 25, 2016 at 12:18 Forivin asked Jul 25, 2016 at 12:08 ForivinForivin 15.5k3030 gold badges118118 silver badges211211 bronze badges 7

• Can you explain what you are trying to achieve? – Rajesh Commented Jul 25, 2016 at 12:12
• 1 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 Commented Jul 25, 2016 at 12:13
• The structure is a bit more plicated 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 Commented Jul 25, 2016 at 12:15
• technically it is [10] would be index = 11 – epascarello Commented Jul 25, 2016 at 12:15
• @Forivin If your structure is even more plicated, my point is even more appropriate. – str Commented Jul 25, 2016 at 12:17

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3 Answers 3

Sorted by: Reset to default 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!

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);

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.

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