Combine multiple json to single json using jq - jq

Question

I am new to jq and stuck with this problem for a while. Any help is appreciable.
I have two json files,
In file1.json:
{
"version": 4,
"group1": [
{
"name":"olditem1",
"content": "old content"
}
],
"group2": [
{
"name":"olditem2"
}
]
}
And in file2.json:
{
"group1": [
{
"name" : "newitem1"
},
{
"name":"olditem1",
"content": "new content"
}
],
"group2": [
{
"name" : "newitem2"
}
]
}
Expected result is:
{
"version": 4,
"group1": [
{
"name":"olditem1",
"content": "old content"
},
{
"name" : "newitem1"
}
],
"group2": [
{
"name":"olditem2"
},
{
"name" : "newitem2"
}
]
}
Criterial for merge:
Has to merge only group1 and group2
Match only by name
I have tried
jq -S '.group1+=.group1|.group1|unique_by(.name)' file1.json file2.json
but this is filtering group1 and all other info are lost.

Answer 1

This approach uses INDEX to create a dictionary of unique elements based on their .name field, reduce to iterate over the group fields to be considered, and an initial state created by combining the slurped (-s) input files using add after removing the group fileds to be processed separately using del.
jq -s '
[ "group1", "group2" ] as $gs | . as $in | reduce $gs[] as $g (
map(del(.[$gs[]])) | add; .[$g] = [INDEX($in[][$g][]; .name)[]]
)
' file1.json file2.json
{
"version": 4,
"group1": [
{
"name": "olditem1",
"content": "new content"
},
{
"name": "newitem1"
}
],
"group2": [
{
"name": "olditem2"
},
{
"name": "newitem2"
}
]
}
Demo