I have created a variable {{dlv-cart}} in google tag manager from datalayer, which gives a value (type array) example:

[
  {
    id: "14",
    code: "P00006-2",
    title: "Name Product 01",
    quantity: 2,
    option: {id: "85"},
    price: {withVat: 138, withoutVat: 115, vat: 23, vatRate: 20}
  },
  {
    id: "16",
    code: "P00004",
    title: "Name Product 02",
    quantity: 1,
    option: null,
    price: {withVat: 63.59, withoutVat: 52.99, vat: 10.6, vatRate: 20}
  },
  {
    id: "17",
    code: "P00003-1",
    title: "Name Product 03",
    quantity: 1,
    option: {id: "61"},
    price: {withVat: 16, withoutVat: 13.33, vat: 2.67, vatRate: 20}
  }
]

1.I need function to combine values with "_" "id" and "option.id" = "id_option.id" ...if "option" is null, then just "id") 2. I need to pull value price.WithVat

and get the result:

[
  {
    id: "14_85",
    title: "Name Product 01",
    quantity: 2,
    price: 138
  },
  {
    id: "16",
    title: "Name Product 02",
    quantity: 1,
    price: 63.59
  },
  {
    id: "17_61",
    title: "Name Product 03",
    quantity: 1,
    price: 16
  }
]

Thank you.