Convert nested JSON array to CSV

[bryceschober]

Given JSON input including an array, like:

{
  "config": {
    "this": 1,
    "that": "something"
  },
  "data": [
    {
      "a": 30,
      "b": 123.4
    },
    {
      "a": 42,
      "b": 432.1
    },
    ...
  ]
}

How would I select only the "data" array for processing? For example, something as "simple" as producing a CSV like:

a,b
30,123.4
42,432.1

I feel this this would be a very common use-case for a tool like this, and I have failed to find the answer I'm looking for in the documentation, so I conclude that I must not be using the correct terminology to find my answer.

[johnkerl]

Hi @bryceschober !

Definitely jq .data myfile.json works :)

If data were an object you could do mlr --json put '$* = $data'

The best I can come up with is

mlr --from myfile.json --j2p put -q '
  begin {
    @records = []
  }

  for (i, row in $data) {
    @records[i] = row
  }

  end {
    for (record in @records) {
      emit record
    }
  }
'

but that's super-wordy .........

[aborruso]

Definitely jq .data myfile.json works :)

jq and miller :)

<input.json jq -c '.data[]' | mlr --ijsonl --ocsv cat

[bryceschober]

Okay, well I'm not that bad at searching docs!

That missing from Miller begs the typical question: "How hard could that be?" 😄