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Json – Recursively remove all keys with empty arrays and objects in JQ

I have the following JSON input:

{
  "a": {
    "a": "foo",
    "b": "bar"
  },
  "b": {
    "a": [],
    "b": []
  },
  "c": {},
  "d": [
    "foo",
    "bar"
  ]
}

I want to recursively remove all the keys that point at empty arrays or objects, so that the result looks like:

{
  "a": {
    "a": "foo",
    "b": "bar"
  },
  "d": [
    "foo",
    "bar"
  ]
}

What I’ve come up with is:

jq 'walk(if ((type=="object" or type=="array") and length==0) then empty else . end)'

But this deletes everything but the last array:

{
  "d": [
    "foo",
    "bar"
  ]
}

If I change empty to {"A":1}:

jq 'walk(if ((type=="object" or type=="array") and length==0) then {"A":1} else . end)'

I get what I expect, where the first, populated object remains untouched:

{
  "a": {
    "a": "foo",
    "b": "bar"
  },
  "b": {
    "a": {
      "A": 1
    },
    "b": {
      "A": 1
    }
  },
  "c": {
    "A": 1
  },
  "d": [
    "foo",
    "bar"
  ]
}

So why is it when I instead tell it to replace zero-length arrays and objects with empty that it attacks non-zero-length objects? What am I doing wrong?

Tags:

2

Answers


  1. 0

    Here is one way to do it:

    def f: recurse | select(. == [] or . == {});
until(isempty(f); del(f))

    Online demo

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  2. 0

    remove all the keys that point at empty arrays or objects

    Here’s a solution using walk and IN:

    walk( if type == "object" 
      then with_entries(select(.value | IN([],{}) | not ) ) 
      else . end)
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