Using jq to convert object to key with values - json

Question

I have been playing around with jq to format a json file but I am having some issues trying to solve a particular transformation. Given a test.json file in this format:
[
{
"name": "A", // This would be the first key
"number": 1,
"type": "apple",
"city": "NYC" // This would be the second key
},
{
"name": "A",
"number": "5",
"type": "apple",
"city": "LA"
},
{
"name": "A",
"number": 2,
"type": "apple",
"city": "NYC"
},
{
"name": "B",
"number": 3,
"type": "apple",
"city": "NYC"
}
]
I was wondering, how can I format it this way using jq?
[
{
"key": "A",
"values": [
{
"key": "NYC",
"values": [
{
"number": 1,
"type": "a"
},
{
"number": 2,
"type": "b"
}
]
},
{
"key": "LA",
"values": [
{
"number": 5,
"type": "b"
}
]
}
]
},
{
"key": "B",
"values": [
{
"key": "NYC",
"values": [
{
"number": 3,
"type": "apple"
}
]
}
]
}
]
I have followed this thread Using jq, convert array of name/value pairs to object with named keys and tried to group the json using this expression
jq '. | group_by(.name) | group_by(.city) ' ./test.json
but I have not been able to add the keys in the output.

Answer 1

You'll want to group the items at the different levels and building out your result objects as you want.
group_by(.name) | map({
key: .[0].name,
values: (group_by(.city) | map({
key: .[0].city,
values: map({number,type})
}))
})
Just keep in mind that group_by/1 yields groups in a sorted order. You'll probably want an implementation that preserves that order.
def group_by_unsorted(key_selector):
reduce .[] as $i ({};
.["\($i|key_selector)"] += [$i]
)|[.[]];