jq transform JSON child array objects to delimited string

Question

I want to transform the following input with jq:

{
   "root":[
      {
         "field1":"field1value1",
         "field2":"field2value2",
         "field3Array":[
            {
               "prop1":"prop1_value1"
            }
         ]
      },
      {
         "field1":"field1value3",
         "field2":"field2value4",
         "field3Array":[
            {
               "prop1":"prop1_value3"
            },
            {
               "prop1":"prop1_value4"
            }
         ]
      }
   ]
}

Output should be:

[
  {
    "field1": "field1value1",
    "field2": "field2value2",
    "field3Array": "prop1_value1"
  },
  {
    "field1": "field1value3",
    "field2": "field2value4",
    "field3Array": "prop1_value3,prop1_value4"
  }
]

I use this jq filter so far:

[.root[] | {field1, field2, field3Array: .field3Array[].prop1}]

but I don't know how to join the array property "prop1" to a comma-delimited string "prop1_value3,prop1_value4".

https://jqplay.org/s/CR8mGBX8Dz

Aaron · Accepted Answer · 2018-12-03 16:12:25Z

1

You need to map the objects contained in the field3Array to their string values and join the resulting array :

.root | map({field1, field2, field3Array: .field3Array | map(.prop1) | join(",")})

You can try it here.

It can be somewhat simplified in the following where we update the .field3Array in-place instead of recreating a whole object :

.root | map(.field3Array |= (map(.prop1) | join(",")))

You can try it here.

If you're unfamiliar with the map function, the following would have worked as well :

[.root[] | {field1, field2, field3Array: [ .field3Array[] | .prop1 ] | join(",")}]

You can try it here.

edited Dec 3, 2018 at 16:12

answered Dec 3, 2018 at 15:22

Aaron

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