How to transform the Array of object to an object in Kotlin

Question

I have a list of object

temp (1_id='I4509635', 2_id='I4406660', 3_id='I1111')
temp (1_id='I4509635', 2_id='I4406660', 3_id='I2222')
temp (1_id='I4509635', 2_id='I4406660', 3_id='I3333')  
temp (1_id='I4509635', 2_id='I1222233', 3_id='I14444')

and want to transform the list to an object. Like

"cat": [
    { "id_": "I4509635",
      "children": [
        {
          "id_": "I4406660",
          "children": [
            {
              id : [ "I1111", "I2222", "I3333"]
            }
          ]
        },
        {
          "id_": "I1222233",
          "children": [
            {
              "id: [ "I14444"]
            }
          ]
        }
      ]
    }
  ]

Is the depth limited to 2? plz let us know what you have tried and if you are facing any issue. — sidgate
– sidgate, Commented Jun 20, 2022 at 12:06

lukas.j · Accepted Answer · 2022-07-25 14:38:12Z

1

I'm not sure I understand your question, you result object is neither a valid Kotlin object nor valid JSON.

data class Ftemp(val Wert_1_id: String, val Wert_2_id: String, val Wert_3_id: String)

val list = listOf(
  Ftemp("I4509635", "I4406660", "I1111"),
  Ftemp("I4509635", "I4406660", "I2222"),
  Ftemp("I4509635", "I4406660", "I3333"),
  Ftemp("I4509635", "I1222233", "I14444")
)

This will give you the data structured in the same way as in your post:

val result = list
  .groupBy { it.Wert_1_id }
  .map { (key, value) -> key to value
    .map { it.Wert_2_id to it.Wert_3_id }
    .groupBy { it.first }
    .map { (key, value) -> key to value.map { it.second } }
  }

This will give you the data structured in the same way as in your post, but with the maps indicating ids and children:

val cat = list
  .groupBy { it.Wert_1_id }
  .map { (key, value) ->
    mapOf(
      "id_" to key,
      "children" to value
        .map { it.Wert_2_id to it.Wert_3_id }
        .groupBy { it.first }
        .map { (key, value) ->
          mapOf(
            "id_" to key,
            "children" to mapOf("id" to value.map { it.second })
          )
        }
    )
  }

edited Jul 25, 2022 at 14:38

answered Jun 20, 2022 at 14:24

lukas.j

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1 Comment

gidds Over a year ago

Also worth pointing out that while nested maps may be a reasonable representation of an arbitrary object tree, and fairly straightforward to create, they're very awkward and fragile to work with. It's usually better to convert instead to fully-fledged objects (e.g. of data classes); that gives you the benefits of type safety, compile-time type checking and inference, better performance, much more readable code, &c.

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