Create a new json string from jq output elements

Question

My jq command returns objects in brackets but without comma separators. But I would like to create a new json string from it.

This call finds all elements of arr that have a FooItem in them and then returns texts from the nested array at index 3:

jq '.arr[] | select(index("FooItem")) | .[3].texts'

on this json (The original has more elements ):

 {
      "arr": [
        [
          "create",
          "w199",
          "FooItem",
          {
            "index": 0,
            "texts": [
              "aBarfoo",
              "avalue"
            ]
          }
        ],
        [
          "create",
          "w200",
          "NoItem",
          {
            "index": 1,
            "val": 5,
            "hearts": 5
          }
        ],
        [
          "create",
          "w200",
          "FooItem",
          {
            "index": 1,
            "texts": [
              "mybarfoo",
              "bValue"
            ]
          }
        ]
    ]
    }

returns this output:

[
  "aBarfoo",
  "avalue"
]
[
  "mybarfoo",
  "bValue"
]

But I'd like to create a new json from these objects that looks like this:

{
    "arr": [
        [
            "aBarfoo",
            "avalue"
        ],
        [
            "mybarfoo",
            "bValue"
        ]
    ]
}

Can jq do this?

EDIT

One more addition: Considering that texts also has strings of zero length, how would you delete those/not have them in the result?

"texts": ["",
          "mybarfoo",
          "bValue",
          ""
          ]

peak · Accepted Answer · 2019-01-01 14:23:16Z

2

You can always embed a stream of (zero or more) JSON entities within some other JSON structure by decorating the stream, that is, in the present case, by wrapping the STREAM as follows:

{ arr: [ STREAM ] }

In the present case, however, we can also take the view that we are simply editing the original document, and accordingly use a variation of the map(select(...)) idiom:

.arr |= map( select(index("FooItem")) | .[3].texts)

This latter approach ensures that the context of the "arr" key is preserved.

Addendum

To filter out the empty strings, simply add another map(select(...)):

.arr |= map( select(index("FooItem"))
             | .[3].texts | map(select(length>0)))

edited Jan 1, 2019 at 14:23

answered Dec 31, 2018 at 14:58

peak

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5 Comments

tzippy Over a year ago

Thank you! it works! However I will definitely have to wrap my head around it to understand it.

tzippy Over a year ago

Is there a way to rename the array arr in the output ?

peak Over a year ago

Of course. Using the first approach, you just specify the alternative name. Using the second approach, you could for example write: .newname = (.arr | map(...)) | del(.arr)

tzippy Over a year ago

Thank you @peak. I had one more final addition, but did not want to ask it in the comments, so I made an edit to the question. Maybe you can help me out one more time.

tzippy Over a year ago

Thanks for the addendum!!

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