How to transform list of objects into object of lists using jq?

Question

Let's say I have some JSON that looks like:

[
    {"foo": "apple", "bar": 42},
    {"foo": "pear", "bar": 13},
    {"foo": "apple", "bar": 666}
]

How can I transform it into something like:

{
   "apple": [42, 666],
   "pear": [13],
}

grouping the bars by the foos?

So far, I've tried using jq's group_by(...) function which gave me:

[
  [{"foo": "apple", "bar": 42}, {"foo": "apple", "bar": 666}],
  [{"foo": "pear", "bar": 13}]
]

which is a start but not exactly what I'm looking for.

peak · Accepted Answer · 2021-02-09 21:17:13Z

2

A simple and efficient solution would avoid group_by, the implementation of which currently entails a sorting operation:

reduce .[] as $x ({}; .[$x.foo] += [$x.bar])

answered Feb 9, 2021 at 18:39

peak

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Comments

Inian · Accepted Answer · 2021-02-09 18:37:36Z

2

You could use group_by and do the transformation after that, i.e. form the key with .foo and add all the .bar's

group_by(.foo)[] | { (.[0].foo): [.[].bar] }

answered Feb 9, 2021 at 18:37

Inian

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