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William Pursell
William Pursell

Reputation: 212684

How to conditionally do a recursive merge?

I'd like to conditionally do a recursive merge. That is, if a key exists in the second object, I'd like to use it to override values in the first. For example, this does what I want:

$ echo '{"a":"value"}{"bar": {"a":"override"}}' | jq -sS '.[0] * if (.[1].foo|length) > 0 then .[1].foo else {} end'
{
  "a": "value"
}
$ echo '{"a":"value"}{"foo": {"a":"override"}}' | jq -sS '.[0] * if (.[1].foo|length) > 0 then .[1].foo else {} end'
{
  "a": "override"
}

In the first example, the second object does not contain a "foo" key, so the override does not happen. In the 2nd example, the second object does contain "foo", so the value is changed. (In my actual use, I always have 3 objects on the input and sometimes have a 4th which may override some of the previous values.)

Although the above works, it seems absurdly ugly. Is there a cleaner way to do this? I imagine something like jq -sS '.[0] * (.[1].foo ? .[1].foo : {}) or similar.

Upvotes: 0

Views: 65

Answers (1)

oguz ismail
oguz ismail

Reputation: 50815

With -n flag specified on the command line this should do the trick:

reduce inputs as $in (input; . * ($in.foo // {}))

jqplay demo

Upvotes: 2

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