How can I map items together in a json structure with jq? - json

Question

I have a json structure that looks like this:
{
"lorry1": {
"box1": [
{"item": "shoes", "state": "new"},
{"item": "snacks", "state": "new"}
],
"box2": [
{"item": "beer", "state": "cold"},
{"item": "potatoes"}
]
},
"lorry2": {
"box1": [
{"item": "shoes", "state": "new"},
{"item": "snacks", "state": "new"}
],
"box2": [
{"item": "beer", "state": "lukewarm"}
]
}
}
Now I want to know where I can find shoes:
I could come up with this jq query:
to_entries | select(.[].value | .[][].item=="shoes") | map({"lorry": "\(.key)" })
But that only gives me the lorries. Useful, but not quite there yet. I'd like to know the box they're in as well.
I came up with this, but it obviously is not correct:
to_entries | select(.[].value | .[][].item=="shoes") | keys as $box |map({"lorry": "\(.key)", "box": $box })
The answer I'd like to get is lorry1, box1 and lorry2, box1.
Even better yet: I'd like to find all items and provide the information, like this:
"shoes": [ {"lorry1", "box1"}, {"lorry2", "box1" } ],
"snacks": [ {"lorry1", "box1"}, {"lorry2", "box1"} ],
"beer": [ {"lorry1", "box2"}, {"lorry2", "box2"} ],
"potatoes": [ {"lorry1", "box2"} ]
but that may be asking a bit too much :)

Answer 1

This looks like a overkill to me but it does the job.
[path(.[][][].item) as $p | [$p, getpath($p)]] |
group_by( .[1] ) |
map({(.[0][1]): (. | map([.[0][0,1]]))})|
add
Save the above jq filter in file item_in.jq and run it as jq --from-file item_in.jq. Passing your input to this gives the following output:
{
"beer": [
[
"lorry1",
"box2"
],
[
"lorry2",
"box2"
]
],
"potatoes": [
[
"lorry1",
"box2"
]
],
"shoes": [
[
"lorry1",
"box1"
],
[
"lorry2",
"box1"
]
],
"snacks": [
[
"lorry1",
"box1"
],
[
"lorry2",
"box1"
]
]
}
The initial transformation was to dump leaves and their paths from the input JSON tree.
See
https://github.com/stedolan/jq/issues/78#issuecomment-17819519

Answer 2

The answer I'd like to get is lorry1, box1 and lorry2, box1
In this case, you can get it with:
path(.. | select(.item? == "shoes"))
Which returns:
["lorry1","box1",0]
["lorry2","box1",0]
These are the paths in your object that will lead to an object which .item property is set to "shoes"

Answer 3

Here's a generic solution that does not assume the "items" are in arrays, or even that the values associated with the "item" keys are always strings:
jq -c '. as $in
| [paths as $p | select($p[-1] == "item") | $p]
| group_by(. as $p | $in|getpath($p))
| .[]
| (.[0] as $p | $in | getpath($p)) as $v
| {($v|tostring): ( map(.[:-1] | if .[-1] | type == "number" then .[:-1] else . end)) }
'
Output
With your input:
{"beer":[["lorry1","box2"],["lorry2","box2"]]}
{"potatoes":[["lorry1","box2"]]}
{"shoes":[["lorry1","box1"],["lorry2","box1"]]}
{"snacks":[["lorry1","box1"],["lorry2","box1"]]}
If you want the output as a single JSON object, then collect the above into an array and use add.