How to use jq to produce multiple JSON objects?

Question

How would one transform a JSON object into several derived JSON objects with jq ?

Example input:

[
  {
     "id": 1,
     "a": "value-in-a",
     "b": "value-in-b"
  },
  {
     "id": 2,
     "c": "value-in-c"
  }
]

Expected output:

[
  {
     "id": "1",
     "value": "value-in-a"
  },
  {
     "id": "1",
     "value": "value-in-b"
  },
  {
     "id": "2",
     "value": "value-in-c"
  }
]

Here the output is an array with 3 elements. First 2 elements are transformed using the first element in the input array. Third element is produced from second element in the input array.

I assume to achieve there will need to be several steps:

a) Construct 2 objects from single JSON object input. Aassume this can be done using variables. First assign input object into variable, then construct object with value a and then with value b. Not sure how to make JQ return several constructed JSON objects.

b) Conditionals will need to be used to not produce an object if a , or b , or c is missing. This can probably be done using 'alternative' operator or if-then-else

Answer 1

You can iterate over the other keys using del and keys_unsorted :

jq 'map({id, value: (del(.id) | .[keys_unsorted[]])})'

[
  {
    "id": 1,
    "value": "value-in-a"
  },
  {
    "id": 1,
    "value": "value-in-b"
  },
  {
    "id": 2,
    "value": "value-in-c"
  }
]

Demo