How to group by in jq?

Question

Here's the json document

[
    {"name": "bucket1","clusterName":"cluster1"},
    {"name": "bucket2","clusterName":"cluster1"},
    {"name": "bucket3","clusterName":"cluster2"},
    {"name": "bucket4","clusterName":"cluster2"}
]

And I want to convert it to

[
{"clusterName": "cluster1", buckets:[{"name": "bucket1"}, {"name": "bucket2"}]},
{"clusterName": "cluster2", buckets:[{"name": "bucket1"}, {"name": "bucket2"}]},
]

How do I do that in jq?

Answer 1

cat doc.json | jq '[group_by(.clusterName)[] | { clusterName: .[0].clusterName, "buckets": [.[] | { name: .name } ]}]'

Should do what you want. Now with an array around as well.

Answer 2

Using map makes for quite a tidy answer:

group_by(.clusterName)
| map( {clusterName: .[0].clusterName,
        buckets: map( {name} ) } )