CODEWITHSUNDEEP
jsonmergejq
Christian Bongiorno
Christian Bongiorno

Reputation: 5648

in jq, how to merge an array of object into 1 object with an array of values

Let's say I have this json:

[
  {
    "first": 12355,
    "second": "abc"
  },
  {
    "first": 89010,
    "second": "def"
  },
  {
    "first": 23423,
    "second": "hij"
  },
  {
    "first": 23456,
    "second": "klm"
  },
  {
    "first": 11111,
    "second": "nop"
  }
]

And I would like (a generic form) that merges them into 1 object where the value of each key is merged into an array of the corresponding values:

{
    "first" : [12355,89010,23423,23456,11111],
    "second" : ["abc","def","hij","klm","nop"]
}

I was trying this, but it produces no output at all.

reduce .[] as $final (
    {};
    ((. | keys) as $k |
        map(
            ( (.[$k] // []) += ($final[$k] // []))
        )
    )
)

Upvotes: 1

Views: 75

Answers (2)

pmf
pmf

Reputation: 36391

I'd use to_entries (to access keys and values) as part of the iteration:

reduce (.[] | to_entries[]) as $e ({}; .[$e.key] += [$e.value])

Demo

Here's another way using group_by to bring the matching items together:

map(to_entries[]) | group_by(.key) | map({(first.key): map(.value)}) | add

Demo

Output:

{
  "first": [
    12355,
    89010,
    23423,
    23456,
    11111
  ],
  "second": [
    "abc",
    "def",
    "hij",
    "klm",
    "nop"
  ]
}

Note: These solutions expect all input objects to have the same set of keys. Missing keys in single objects will lead to shortened, thus potentially misaligned output arrays. To readjust the arrays by pitching in null values, normalize the objects before destructuring them into entries by reconstructing them using a pre-defined set of keys, e.g. {first, second}:

reduce (.[] | {first, second} | to_entries[]) as $e …
# or
map({first, second} | to_entries[]) | group_by(.key) …

If, however, the actual set of keys is dynamic or unknown, screen and collect them first, e.g. using (map(keys[]) | unique) as $keys, then normalize based on that set using pick(.[$keys[]]) (pick was introduced with jq 1.7; older versions could use .[$keys[]] //= null instead):

(map(keys[]) | unique) as $keys
| reduce (.[] | pick(.[$keys[]]) | to_entries[]) as $e …
# or
(map(keys[]) | unique) as $keys
| map(pick(.[$keys[]]) | to_entries[]) | group_by(.key) …

Upvotes: 3

peak
peak

Reputation: 116957

Or for simplicity, consider using transpose, e.g.

map([.[]]) | transpose | {first: first, second: .[1]}

Upvotes: 0

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