reduce-object-to-just-entries-of-a-specific-type.md

Reduce Object To Just Entries Of A Specific Type

Let's say I have a large JSON data file with a ton of top-level fields of varying types. It can be hard to wade through it as is. The jq utility can help. I can filter a JSON object down to just the fields of a certain type.

For instance, I may want to start with a view of the JSON that is restricted to just the values of type array.

To do this, I need to use a couple different jq helper functions.

jq '. | to_entries | map(select(.value | type | match("array"))) | from_entries' data.json

This starts with to_entries to convert an object into an array of key-value pairs. I then map over those pairs selecting just the pairs whose value matches the "array" type. I then use from_entries to turn the reduced array back into an object.

There is a less verbose way to do the above. The to_entries and from_entries can be collapsed into a with_entries that wraps the map call.

jq '. | with_entries(map(select(.value | type | match("array")))' data.json