Intersecting nested JSON documents with jq - json

Question

I'm looking for a general approach to intersect two nested JSON-objects, in order to retrieve all common key-value pairs.
Given the following JSON-documents
{
"a": 0,
"b": [
"ba",
{
"bb": {
"bba": "a",
"bbc": [1, 2]
}
},
{
"bc": {
"bca": [2],
"bcb": 5
}
}
],
"c": 1
}
and
{
"a": 1,
"b": [
"ba",
{
"bb": {
"bba": "a",
"bbc": [1,3]
}
}
],
"c": 1
}
I want to find their intersection.
I expect to get the following JSON-document which only contains those key-value-pairs JSON-objects that are present in both inputs:
{
"b": [
"ba",
{
"bb": {
"bba": "a",
"bbc": [1]
}
}
],
"c": 1
}
I looked into jq's documentation, but could not find a hint on how to do this.
My tries to use the minus-operator were unsuccessful yielding object ... and object cannot be subtracted.
cat obj-list.txt | jq -c '.[1] - (.[0] - .[1])'
Can you give me some hints on how to accomplish a intersection of nested JSON-objects with jq?
Thank you already in advance for helping me out.
Update:
Given that the JSON-objects do not have the exact same structure, but differ like a = {"a": [{"aa":1]}, b = {"a": 0} for example. I'm interested in a solution on how to add error checking to catch Cannot index number with string-errors and the like?

Answer 1

Assuming $a holds the contents of one of your JSON entities and $b holds the other, then the following will perform the type of intersection you describe:
reduce ($a|paths) as $p (null;
($a|getpath($p)) as $va
| [try ($b|getpath($p)) // empty] as $vb
| if ($vb | length > 0) and ($va == $vb[0])
then setpath($p;$va) else . end)
You may however wish to explore variations of this, e.g. if there is nothing in common.
Footnote 1:
The above is easily adapted to similar problems. For example, if the common structure is all that matters:
def structural_intersection($a;$b):
reduce ($a|paths|select(.[-1]|type=="string")) as $p (null;
($a|getpath($p)) as $va
| [try ($b|getpath($p)) // empty] as $vb
| if ($vb | length > 0)
then setpath($p;null) else . end) ;
Footnote 2:
To handle arrays using array-intersection, you might wish to consider the following, but please be aware that in some cases, this hybrid approach will probably produce results that you might not expect:
def special_intersection($a;$b):
def i(x;y): x - (x-y);
reduce ($a|paths) as $p (null;
($a|getpath($p)) as $va
| [try ($b|getpath($p)) // empty] as $vb
| if ($vb | length > 0)
then if ($va == $vb[0])
then setpath($p;$va)
elif ($va|type == "array") and ($vb[0]|type) == "array"
then setpath($p; i($va; $vb[0]))
else . end
else . end) ;