Flatten a hierarchical JSON array using JQ

Question

Can anyone help me get the correct jq command to flatten the below example? I've seen a few other posts and I'm hacking away at it but can't seem to get it. I'd greatly appreciate any help.

Input:

[
    {
        "name": "level1",
        "children": [
            {
                "name": "level2",
                "children": [
                    {
                        "name": "level3-1",
                        "children": []
                    },
                    {
                        "name": "level3-2",
                        "children": []
                    }
                ]
            }
        ]
    }
]

Output:

[
    {
        "displayName": "level1",
        "parent": ""
    },
    {
        "displayName": "level2",
        "parent": "level1"
    },
    {
        "displayName": "level3-1",
        "parent": "level2"
    },
    {
        "displayName": "level3-2",
        "parent": "level2"
    }
]

peak · Accepted Answer · 2020-07-31 20:01:49Z

2

Here's a straightforward solution that does not involve a helper function and actually solves a more general problem. It is based on the idea of beginning by adding a "parent" key to each child, and then using .. to collect all the name/parent pairs.

So first consider:

[ walk(if type=="object" and has("children")
       then .name as $n | .children |= map(.parent = $n)
       else . end)
  | ..
  | select(type=="object" and has("name"))
  | {displayName: .name, parent}
]

This meets the requirements except that for the top-level (parentless) object, it produces a .parent value of null. That would generally be more JSON-esque than "", but if the empty string is really required, one has simply to replace the last non-trivial line above by:

| {displayName: .name, parent: (.parent // "")}

edited Jul 31, 2020 at 20:01

answered Jul 31, 2020 at 18:30

peak

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Comments

oguz ismail · Accepted Answer · 2020-07-31 15:24:55Z

1

With a simple recursive function:

def f: .name as $parent | .children[] | {$parent, displayName: .name}, f;
[ {name: "", children: .} | f ]

^{Online demo}

answered Jul 31, 2020 at 15:24

oguz ismail

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