Convert an array of arrays as items to object with objects as items

Question

I have an array like this:

var arr = [
    ['a1','b1','c1','d1'],
    ['a1','e1','i1','j1'],
    ['a1','f1','k1','l1'],
    ['a1','g1','m1','n1'],
    ['a1','h1','o1','p1'],
    ['a2','b2','c2','d2'],
    ['a2','e2','i2','j2'],
    ['a2','f2','k2','l2'],
    ['a2','g2','m2','n2'],
    ['a2','h2','o2','p2']
];

and I want to convert it to an object like this:

var converted_arr = {
    'a1':{
        'b1':['c1','d1'],
        'e1':['i1','j1'],
        'f1':['k1','l1'],
        'g1':['m1','n1'],
        'h1':['o1','p1'],
    },
    'a2':{
        'b2':['c2','d2'],
        'e2':['i2','j2'],
        'f2':['k2','l2'],
        'g2':['m2','n2'],
        'h2':['o2','p2'],
    }
};

As you can see all the items of the first array (arr) are arrays and it's item in these arrays are strings or numbers or both.
One of the examples I have tried is the following:

var obj = {};
$.each(arr,function(a)
{
    obj[a[0]][a[1]] = a.slice(2);
});

But it produces nothing.
Can someone help me out?

Please post the code which you have tried. And where exactly you are stuck? — Sunil Chaudhary
– Sunil Chaudhary, Commented Mar 3, 2019 at 12:32
Answered below. Please consider variable naming carefully. converted_arr is a poor choice because arr suggests that the value is an array when actually it is an object. converted would be a poor choice because it's essentially meaningless. Choose a name that's indicative of the purpose/meaning of the value for your final solution. Good luck! — Nick
– Nick, Commented Mar 3, 2019 at 12:50

adiga · Accepted Answer · 2019-03-03 12:48:51Z

3

You could use reduce and destructuring like this:

var arr = [
    ['a1','b1','c1','d1'],
    ['a1','e1','i1','j1'],
    ['a1','f1','k1','l1'],
    ['a1','g1','m1','n1'],
    ['a1','h1','o1','p1'],
    ['a2','b2','c2','d2'],
    ['a2','e2','i2','j2'],
    ['a2','f2','k2','l2'],
    ['a2','g2','m2','n2'],
    ['a2','h2','o2','p2']
];

const newArray = arr.reduce((acc, [key, key2, ...rest]) => {
  acc[key] = acc[key] || {};
  acc[key][key2] = rest
  return acc;
}, {})

console.log(newArray)

answered Mar 3, 2019 at 12:48

adiga

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Comments

Sunil Chaudhary · Accepted Answer · 2019-03-03 17:01:48Z

You are on right track. Just the function usage was wrong. I have reused the code and updated it to make it work fine. For $.each function, the first value is the index (docs) which was the main cause for error.

I have update the code and it works fine.

var arr = [
    ['a1','b1','c1','d1'],
    ['a1','e1','i1','j1'],
    ['a1','f1','k1','l1'],
    ['a1','g1','m1','n1'],
    ['a1','h1','o1','p1'],
    ['a2','b2','c2','d2'],
    ['a2','e2','i2','j2'],
    ['a2','f2','k2','l2'],
    ['a2','g2','m2','n2'],
    ['a2','h2','o2','p2']
];
obj = {}
$.each(arr,function(index)
{
    obj[arr[index][0]] = obj[arr[index][0]] || {}
    obj[arr[index][0]][arr[index][1]] = arr[index].slice(2);
});
console.log(obj)

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

Note: The solution is specific for above requirement. However, it can be generalized as well using recursion.

Hope it helps. Revert for any doubts/clarifications.

Nick · Accepted Answer · 2019-03-03 12:43:35Z

-1

Using reduce in the Lodash library you could do the following, where arr is your input array.

_.reduce(arr, function(acc, val) { var k1 = val[0], k2 = val[1], val = val.slice(2); acc[k1] = acc[k1] || {}; acc[k1][k2] = val; return acc; }, {});

answered Mar 3, 2019 at 12:43

Nick

1,44212 silver badges15 bronze badges

2 Comments

StudioTime Over a year ago

You're suggesting a library the OP has not mentioned, plus, this is available now in most modern browsers natively, without a library.

Nick Over a year ago

Granted Darren, however the OP didn't say that he's targeting a modern browser, lodash is ubiquitous so he's probably using it already, and he will discover a useful library that will stand him in good stead if he isn't aware of it already. So I went for the safer and potentially more educational version. The expressiveness of the more recent JS is a joy to behold though!

Elegie · Accepted Answer · 2019-03-03 14:46:23Z

Here's a simple example working for a list of lists (as per your examples), with the min size of leaf arrays being passed as parameter (in your case set to 2).

The mapping extracts a key and accumulates arrays, while the normalizing reduces the arrays recursively, until a satisfying result has been reached.

var arr = [
    ['a1','b1','c1','d1'],
    ['a1','e1','i1','j1'],
    ['a1','f1','k1','l1'],
    ['a1','g1','m1','n1'],
    ['a1','h1','o1','p1'],
    ['a2','b2','c2','d2'],
    ['a2','e2','i2','j2'],
    ['a2','f2','k2','l2'],
    ['a2','g2','m2','n2'],
    ['a2','h2','o2','p2']
];

console.log(transform(arr, 2));

function transform(input, minSize) {

  return normalize(map(input, {}), minSize);

  function map(input, result) {
    for (var ii = 0; ii < input.length; ii++) {
      var row = input[ii];
      if (row.length == 0) {
        continue;
      }

      var first = row[0];
      var list = result[first] || (result[first] = []);
      list.push(cdr(row));
    }
    return result;
  }

  function normalize(result, minSize) {
    for (var key in result) {
      var list = result[key];
      if (list.length == 0) {
        continue;
      }
      var first = list[0];
      if (list.length == 1 && first.length <= minSize) {
        result[key] = first;
        continue;
      }
      result[key] = transform(list, minSize);
    }
    return result;
  }

  function cdr(list) {
    var result = [];
    for (var ii = 1; ii < list.length; ii++) {
      result.push(list[ii]);
    }
    return result;
  }
}

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