How to use jq to reconstruct complete contents of json file, operating only on part of interest?

Question

All the examples I've seen so far "reduce" the output (filter out) some part. I understand how to operate on the part of the input I want to, but I haven't figured out how to output the rest of the content "untouched".

The particular example would be an input file with several high level entries "array1", "field1", "array2", "array3" say. Each array contents is different. The specific processing I want to do is to sort "array1" entries by a "name" field which is doable by:

jq '.array1 | sort_by(.name)' test.json

but I also want this output as "array1" as well as all the other data to be preserved.

Example input:

{
    "field1": "value1",
    "array1":
        [
            { "name": "B", "otherdata": "Bstuff" },
            { "name": "A", "otherdata": "Astuff" }
        ],
    "array2" :
        [
            array2 stuff
        ],
    "array3" :
        [
            array3 stuff
        ]
}

Expected output:

{
    "field1": "value1",
    "array1":
        [
            { "name": "A", "otherdata": "Astuff" },
            { "name": "B", "otherdata": "Bstuff" }
        ],
    "array2" :
        [
            array2 stuff
        ],
    "array3" :
        [
            array3 stuff
        ]
}

I've tried using map but I can't seem to get the syntax correct to be able to handle any type of input other than the array I want to be sorted by name.

Answer 1

Whenever you use the assignment operators (=, |=, +=, etc.), the context of the expression is kept unchanged. So as long as your top-level filter(s) are assignments, in the end, you'll get the rest of the data (with your changes applied).

In this case, you're just sorting the array1 array so you could just update the array.

.array1 |= sort_by(.name)