Grouping data with JOLT transformation

I am new to JOLT language and I am having a little headache with a transformation. My JSON input is this one

[
  {
    "table": 0,
    "_time": "2024-05-08T10:33:48.14Z",
    "_value": 40976,
    "parameter": "A",
    "station": "ABC",
    "stationName": "AABBCC"
  },
  {
    "table": 0,
    "_time": "2024-05-08T10:34:33.372Z",
    "_value": 42009,
    "parameter": "A",
    "station": "ABC",
    "stationName": "AABBCC"
  },
  {
    "table": 1,
    "_time": "2024-05-08T10:33:48.141Z",
    "_value": 22091,
    "parameter": "B",
    "station": "XYZ",
    "stationName": "XXYYZZ"
  },
  {
    "table": 1,
    "_time": "2024-05-08T10:34:10.231Z",
    "_value": 21968,
    "parameter": "B",
    "station": "XYZ",
    "stationName": "XXYYZZ"
  }
]

And I am expecting this:

[
  {
    "stationName": "AABBCC",
    "content": [
      {
        "table": 0,
        "_time": "2024-05-08T10:33:48.14Z",
        "_value": 40976,
        "parameter": "A",
        "station": "ABC"
      },
      {
        "table": 0,
        "_time": "2024-05-08T10:34:33.372Z",
        "_value": 42009,
        "parameter": "A",
        "station": "ABC"
      }
    ]
  },
  {
    "stationName": "XXYYZZ",
    "content": [
      {
        "table": 1,
        "_time": "2024-05-08T10:33:48.141Z",
        "_value": 22091,
        "parameter": "B",
        "station": "XYZ"
      },
      {
        "table": 1,
        "_time": "2024-05-08T10:34:10.231Z",
        "_value": 21968,
        "parameter": "B",
        "station": "XYZ"
      }
    ]
  }
]

As you can see, I need the following:

Group de data in diferente arrays, based on "station"
Move "stationName" one level up, out of the array
All the JSON need to be an array

The farthest i can go is with this spec

[
  {
    "operation": "shift",
    "spec": {
      "*": "@station"
    }
    },
  {
    "operation": "shift",
    "spec": {
      "@": "[]"
    }
  }
]

That gives me this:

[
  {
    "ABC": [
      {
        "table": 0,
        "_time": "2024-05-08T10:33:48.14Z",
        "_value": 40976,
        "parameter": "A",
        "station": "ABC",
        "stationName": "AABBCC"
      },
      {
        "table": 0,
        "_time": "2024-05-08T10:34:33.372Z",
        "_value": 42009,
        "parameter": "A",
        "station": "ABC",
        "stationName": "AABBCC"
      }
    ],
    "XYZ": [
      {
        "table": 1,
        "_time": "2024-05-08T10:33:48.141Z",
        "_value": 22091,
        "parameter": "B",
        "station": "XYZ",
        "stationName": "XXYYZZ"
      },
      {
        "table": 1,
        "_time": "2024-05-08T10:34:10.231Z",
        "_value": 21968,
        "parameter": "B",
        "station": "XYZ",
        "stationName": "XXYYZZ"
      }
    ]
  }
]

I dont know if what I am looking for is possible or not to be honest. It is important to clarify that i need to generalize the expression, because the "station" is not always the same.

At least. I would accept this one:

[
  {
    "stationName": "XXYYZZ",
    "ABC": [
      {
        "table": 0,
        "_time": "2024-05-08T10:33:48.14Z",
        "_value": 40976,
        "parameter": "A",
        "station": "ABC"
      },
      {
        "table": 0,
        "_time": "2024-05-08T10:34:33.372Z",
        "_value": 42009,
        "parameter": "A",
        "station": "ABC"
      }
    ],
    "XYZ": [
      {
        "table": 1,
        "_time": "2024-05-08T10:33:48.141Z",
        "_value": 22091,
        "parameter": "B",
        "station": "XYZ"
      },
      {
        "table": 1,
        "_time": "2024-05-08T10:34:10.231Z",
        "_value": 21968,
        "parameter": "B",
        "station": "XYZ"
      }
    ]
  }
]

But i really prefer the previous one

Thank you so much!

Solution

Your approach is pretty good but need to take stationName out, not to keep all nested, so we should separately manipulate the stationName attribute. @1,stationName on the RHS will be useful during this manipulation such as

[
  {
    "operation": "shift",
    "spec": {
      "*": {
        "stationName": "@1,stationName.&", //separate the stationName vs. others
        "*": "@1,stationName.content.&1.&"
      }
    }
  },
  {
    "operation": "shift",
    "spec": {
      "*": {
        "stationName": {
          "0": "&2.&1" //pick only one componet from the array 
        },
        "content": {
          "*": {
            "*": "&3.&2[#2].&" //&2 means grabbing the lieral "content" after going 2 levels up the tree 
          }
        }
      }
    }
  },
  {
    "operation": "shift",
    "spec": {
      "*": "[]"
    }
  }
]

the demo on the site https://jolt-demo.appspot.com/ is :