How can I group an array of objects by key and create another object inside

Question

Does anyone know how to group an array of objects by an object key and then create a new array of objects based on the grouping? For example, I have an array of Build objects as below and I want to group by products and create another object of colors and price based on that.

build = [
    {
        'Product': 'Cabinets',
        'Color': 'Blue',
    }, 
    {
        'Product': 'CounterTop',
        'Color': 'White',
    }, 
    {
        'Product': 'Cabinets',
        'Color': 'Yellow',
    }, 
    {
        'Product': 'Cabinets',
        'Color': 'Yellow',
    }
]

And I want it like this

[
  {
     'Product':'Cabinet',
     'color' : { 'Blue','Yellow' }
  },
  {
     'Product':'CounterTop',
     'color' : { 'White' }
  }
]

I wrote a code to archive it but I am not getting the result as expected.

build.forEach(pr => {
                if (pr.Product in result) {
                    result[pr['Product']]['Color'] = pr['Color'];
                }
                else {
                    result[pr['Product']] = {
                        'Product': pr['Product'],
                        'Color': pr['Color'] 
                    }
                }
            });

Above code returns

 [
  {
     'Product':'Cabinet',
     'color' : 'Yellow' 
  },
  {
     'Product':'CounterTop',
     'color' : 'White'
  }
]

Answer 1

Expecting 'color' : { 'Blue','Yellow' } in your output is wrong. Objects are key-value pairs of data.

Instead, you want color to be an array. I adjusted your code:

build.forEach(pr => {
  if (pr.Product in result) {
      result[pr['Product']]['Color'].push(pr['Color']);
  } else {
      result[pr['Product']] = {
          'Product': pr['Product'],
          'Color': [pr['Color']]
      }
  }
});

Now think about how you can prevent duplicate values in the array. @Lissy93's answer helps with that by using findIndex.