Dataweave: How to filter and concatenate values for certain keys in json array

Question

My input is

{
    "value": [
        {
            "FirstName": "LISA",
            "Sku1": 10074895,
            "Sku2": 10074896,
            "Sku3": 10074897
        },
        {
            "FirstName": "JOSE",
            "Sku1": 10128582,
            "Sku2": null,
            "Sku3": null
        }
    ]
}

Output I want is a string concatenating all the SKUs

{
    "value": [
        {
            "FirstName": "LISA",
            "Skus": "10074895, 10074896, 10074897"
        },
        {
            "FirstName": "JOSE",
            "Skus": "10128582"
        }
    ]
}

I'm new to Dataweave and not sure how to do this Thanks in advance

EDIT 1

My input will have more keys than "FirstName", that I will want to exclude

{
    "value": [
        {
            "FirstName": "LISA",
            "Country": "CA",
            "Sku1": 10074895,
            "Sku2": 10074896,
            "Sku3": 10074897
        },
        {
            "FirstName": "JOSE",
            "Country": "CA",
            "Sku1": 10128582,
            "Sku2": null,
            "Sku3": null
        }
    ]
}

This is the solution I have come up with, can someone help fix this solution . The problem is that there is a trailing "," at the end of "Skus" in the output

%dw 2.0
output application/json

fun mapToResponseModel(customObj) = do {
    var skus = createSkus(customObj)
    var withoutSkus = mapWithoutSkus(customObj)
    ---
  withoutSkus ++ { "Skus": skus }
}
    
fun createSkus(customObj) =
    keysOf(customObj) reduce (key, acc = "") ->
        if ((key contains "Sku") and (customObj[key] != null))
            customObj[key] ++ "," ++  acc
        else
            acc

fun mapWithoutSkus(customObj) =
    customObj mapObject (value, key) ->
        if (value != null and !(key contains "Sku"))
            { (key): value }
        else
            {}
---
{
    value: payload.value map (customObj) ->
        mapToResponseModel(customObj)
}

Output

{
  "value": [
    {
      "FirstName": "LISA",
      "Country": "CA",
      "Skus": "10074897,10074896,10074895,"
    },
    {
      "FirstName": "JOSE",
      "Country": "CA",
      "Skus": "10128582,"
    }
  ]
}

Answer 1

For Edit 1 try with the following script:

%dw 2.0
output application/json
var skuValues = payload.value map {
    ($ filterObject (($$) contains "Sku" ) mapObject  {
           a : $
    })
}
---

value: payload.value map {
     "FirstName": $.FirstName,
     "Country" : $.Country,
     "Skus":  skuValues [($$)] filterObject($ != null) pluck $ joinBy ","
}