Reformat an array of objects to an array of key'd arrays

Question

So I am kind of new to Javascript but I am trying to reformat the startArray into the endArray. The startArray is basically an array of order objects, which will always have different orderId's but can have the same companyId. I basically am trying to switch it so it's based on company, and so that for each companyId, there is an array of all of that companies orders. I have been tinkering and trying to figure this out, but to be honest I'm not sure where to start, or if this manipulation is even possible.

I am working out of Google Apps Scripts, which I think is still on ES5 syntax, and I would prefer to stick to vanilla javascript if at all possible.

var startArray = [
    {"companyId" : 1,
     "orderId" : 25,
     "product" : "productA"
     "quantity" : 2,
     "price" : 10,
    },
    {"companyId" : 1,
     "orderId" : 20,
     "product" : "productB"
     "quantity" : 3,
     "price" : 5,
    },
   {"companyId" : 2,
     "orderId" : 15,
     "product" : "productA"
     "quantity" : 5,
     "price" : 10,
    }
 ]

 var endArray = [ {
      '1' = [{"orderId" : 25,
         "product" : "productA"
         "quantity" : 2,
         "price" : 10,},
         {"orderId" : 20,
          "product" : "productB"
          "quantity" : 3,
          "price" : 5,}
      },{
     '2' = [{"orderId" : 15,
          "product" : "productA"
          "quantity" : 5,
          "price" : 10,
         }]
   }]


 ]

Answer 1

If you are fine with result being object and not array, this should do the job:

 var startArray = [ {"companyId" : 1, "orderId" : 25, "product" : "productA", "quantity" : 2, "price" : 10, }, {"companyId" : 1, "orderId" : 20, "product" : "productB", "quantity" : 3, "price" : 5, }, {"companyId" : 2, "orderId" : 15, "product" : "productA", "quantity" : 5, "price" : 10, } ]; var ret = {} startArray.forEach(company => { if (!ret[company.companyId]) { ret[company.companyId] = []; } ret[company.companyId].push(company); }); console.log(ret); 

If you do not have ES6 support, just use classic for in cycle instead of forEach .

Answer 2

Use something like reduce to create a new object, inserting an array as the key of the companyId if it doesn't exist already:

 function reduce(arr, callback, initialVal) { var accumulator = (initialVal === undefined) ? undefined : initialVal; for (var i = 0; i < arr.length; i++) { if (accumulator !== undefined) accumulator = callback.call(undefined, accumulator, arr[i], i, this); else accumulator = arr[i]; } return accumulator; } var startArray = [ {"companyId" : 1, "orderId" : 25, "product" : "productA", "quantity" : 2, "price" : 10, }, {"companyId" : 1, "orderId" : 20, "product" : "productB", "quantity" : 3, "price" : 5, }, {"companyId" : 2, "orderId" : 15, "product" : "productA", "quantity" : 5, "price" : 10, } ]; var endObj = reduce(startArray, function (accum, item) { var companyId = item.companyId; if (!accum[companyId]) accum[companyId] = []; delete item.companyId; accum[companyId].push(item); return accum; }, {}); console.log(endObj);