How to Output Array with groupBy Function

Question

I am using the standard groupBy function, modified by returning [hash] instead of hash. This returns an array of objects.

How can I instead output an array of arrays?

Standard groupBy Function

function groupBy(array, property) {
  var hash = {};
  for (var i = 0; i < array.length; i++) {
    if (!hash[array[i][property]]) hash[array[i][property]] = [];
    hash[array[i][property]].push(array[i]);
  }
  return [hash];
}

Output

[{key1:[array]}, {key2:[array]}, {key3:[array]}]

Desired Output

[[array1], [array2], [array3]]

Ultimately, I would like to run a for each over the output of arrays to pass into another function.

For instance,

let group = groupItemBy(cart, 'id');
console.log(group.length); // should be greater than 1 for multiple indexes

[key2: is invalid JavaScript syntax. Either you want a plain object with named keys or an array. You cannot have some half-half. — trincot
– trincot, Commented Feb 18, 2018 at 15:44
Your key and array are separated by : which is not valid. — Hassan Imam
– Hassan Imam, Commented Feb 18, 2018 at 15:44

trincot · Accepted Answer · 2018-02-18 15:49:53Z

3

Instead of

return [hash];

Do:

return Object.values(hash);

answered Feb 18, 2018 at 15:49

trincot

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2 Comments

KVNA Over a year ago

I'm not sure how to get this to work with nested data. See: jsbin.com/cemedebugu/edit?js,console

trincot Over a year ago

That really is a different question, as there the property does not exist in the objects, but in nested objects. This will also mean you need to better define the function arguments so that it is clear where this property is to be located. If you cannot make it work as you expect, I would suggest posting that as a new question.

Jonas Wilms · Accepted Answer · 2018-02-18 15:49:27Z

0

Assuming you return hash and not [hash] , just get the objects values:

 Object.values(groupItemBy(cart, 'carrierId'))

Alternatively build up the hashtable and the result in parallel:

 function group(array, key){
   const hash = {}, result = [];

   for(const obj of array){
     if(hash[ obj[key] ]){
       hash[ obj[key] ].push(obj);
     } else {
       result.push( hash[ obj[key] ] = [obj]);
    }
  }

  return result;
}

edited Feb 18, 2018 at 15:49

answered Feb 18, 2018 at 15:47

Jonas Wilms

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9 Comments

Hassan Imam Over a year ago

I think OP function is returning an array.

KVNA Over a year ago

I'm not seeing the difference between logging Object.values(groupItemBy(cart, 'carrierId')) and group...

KVNA Over a year ago

Not sure if it's causing problems, but I am actually sorting by a value, so when I return hash and log Object... everything gets put into a single array.

Jonas Wilms Over a year ago

@kvna what do you mean with sorting by a value ?

KVNA Over a year ago

Would you please take a look at this fiddle? jsfiddle.net/04v1uczr

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