Jolt expression to merge 2D array

Question

So I have geo Coordinates and I want to create polygon string that i can insert into Postgres as geometry type. I am using apache Nifi.

Input:

[
  [
    13,
    52
  ],
  [
    13,
    55
  ],
  [
    14,
    15
  ]
]

Expected Output:

POLYGON((13 52, 13 55, 14 15))

I tried with below JOLT but no luck:

[
  {
    "operation": "shift",
    "spec": {
      "*": {
        "*": "[&1].[&0]"
      }
    }
  },
  {
    "operation": "shift",
    "spec": {
      "*": {
        "*": "&"
      }
    }
  },
  {
    "operation": "modify-overwrite-beta",
    "spec": {
      "*": {
        "*": "=join(' ',@(1,&))"
      }
    }
  },
  {
    "operation": "modify-overwrite-beta",
    "spec": {
      "*": "=concat('POLYGON((',@(1,2),'))')"
    }
  }
]

Answer 1

You can convert the current one to this :

[
  { // form independent arrays with keys of indexes taken from the outermost array
    "operation": "shift",
    "spec": {
      "*": {
        "*": "&1"
      }
    }
  },
  { // stringify those arrays
    "operation": "modify-overwrite-beta",
    "spec": {
      "*": "=join(' ',@(1,&))"
    }
  },
  { // generate an array namely "Coord"
    "operation": "shift",
    "spec": {
      "*": {
        "@": "Coord"
      }
    }
  },
  {
    "operation": "modify-overwrite-beta",
    "spec": {
      "Coord": "=join(' ,',@(1,&))",
      "*": "=concat('POLYGON((',@(1,&),'))')"
    }
  }
]

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