How to group and count elements of a JSON file with multiple objects on javascript?

I am very new to javascript, and so far everything was fine until I ran into this dilemma, I need to restructure a JSON file as follows:

{
    firstName: "Joel",
    lastName: "Munz",
    total: 154,
    transaction: "111111",
    articles:[
        {
            sku: "abc123456",
            number: 2,
            price: 65
        },
        {
            sku: "def123456",
            number: 2,
            price: 24
        }
    ]
},
{
    firstName: "Patel",
    lastName: "Dass",
    total: 85,
    transaction: "222222",
    articles: [
        {
            sku: "abc123456",
            number: 1,
            price: 65
        },
        {
            sku: "def123456",
            number: 2,
            price: 10
        }
    ]
}

And my source file has the following structure:

{
    "transactions":[
        {
            "items":[
                {
                    "price":65,
                    "sku":"abc123456"
                },
                {
                    "price":65,
                    "sku":"abc123456"
                },
                {
                    "price":12,
                    "sku":"def123456"
                },
                {
                    "price":12,
                    "sku":"def123456"
                }
            ],
            "total":154,
            "transaction":"111111",
            "customer":{
                "firstName":"Joel",
                "lastName":"Munz"
            }
        },
        {
            "items":[
                {
                    "price":65,
                    "sku":"abc123456"
                },
                {
                    "price":10,
                    "sku":"ghi123456"
                },
                {
                    "price":10,
                    "sku":"ghi123456"
                }
            ],
            "total":85,
            "transaction":"222222",
            "customer":{
                "firstName":"Patel",
                "lastName":"Dass"
            }
        }
    ]
}

what I have tried is the following, but it doesn’t have the structure that I need. I’ve read about using the reduce () forEach () function, but I don’t know how to implement it to match the format I need.

const trans = data.transactions.map(transaction => ({
    "firstName": transaction.customer.firstName,
    "lastName": transaction.customer.lastName,
    "total":transaction.total,
    "order_id": transaction.transaction,  //OP
    "articles": {
        "sku":transaction.items.map(Item => Item.sku),
        "number":transaction.items.map(Item => Item.sku).length,
        "price":transaction.items.map(Item => Item.price)}
    }))
console.log(trans);

Any suggestions?
Thanks for the help!