Issue when GroupBy an ArrayList object in Kotlin?-CodePudding

I have issue when I use GroupBy an ArrayList object in Kotlin.

I have JSON like here:

 {
  "securityAccountList": [
    {
      "accountNumber": "001548900001",
      "accountName": "Tjandraningrum",
      "currency": "IDR",
      "debtInstrument": "0",
      "equityInstrument": "0"
    },
    {
      "accountNumber": "001548900001",
      "accountName": "Tjandraningrum",
      "currency": "IDR",
      "debtInstrument": "0",
      "equityInstrument": "0"
    },
    {
      "accountNumber": "001548900001",
      "accountName": "Tjandraningrum",
      "currency": "USD",
      "debtInstrument": "22",
      "equityInstrument": "66"
    }
  ]
}

I generate object by GSON like this:

 data class ContentModel(
        @SerializedName("securityAccountList") var securityAccountList: ArrayList<SecurityAccountList> = arrayListOf()
    ) 

    data class SecurityAccountList(

        @SerializedName("accountNumber") var accountNumber: String? = null,
        @SerializedName("accountName") var accountName: String? = null,
        @SerializedName("currency") var currency: String? = null,
        @SerializedName("debtInstrument") var debtInstrument: String? = null,
        @SerializedName("equityInstrument") var equityInstrument: String? = null

    )

now I want to grouping by field currency and I want result like this

{
  "securityAccountList": [
    {
      "accountNumber": "001548900001",
      "accountName": "Tjandraningrum",
      "currency": "IDR",
      "debtInstrument": "0",
      "equityInstrument": "0"
    },
    {
      "accountNumber": "001548900001",
      "accountName": "Tjandraningrum",
      "currency": "USD",
      "debtInstrument": "22",
      "equityInstrument": "66"
    }
  ]
}

but the result not changed, still 3 securityAccountList, this my code for grouping:

val  newSecurityAccountList= contentModel.securityAccountList
     newSecurityAccountList.groupingBy { it.currency }
     newSecurityAccountList.sortBy { it.currency }

Note: contentModel.securityAccountList is ArrayList of object JSON the newSecurityAccountList not changed value.

please your advice, sorry for my English.

CodePudding user response：

private fun List<SecurityAccountList>.customFilter(): List<SecurityAccountList> =
    groupBy { it.currency }.map {
// HERE you can do whaterver you need.
        it.value
            .filter { item-> item.currency >= 0 }
            .maxByOrNull { item-> item.accountName.length }
    }.filterNotNull()

Using in code

val returnlist = yourListBeforeFilter.customFilter()

For more details tell us what exactly you need. You can as well use here sortBy

CodePudding user response：

It sounds like you are expecting groupingBy to modify the list. In fact it won't, but will instead return a new Grouping object which can be used to gather the results into a new, different list.

It can be confusing, because sortBy does mutate the list, whereas the similar-looking groupBy and groupingBy functions return a new object or copy and don't mutate the original.

The best way to be sure whether a function is going to mutate the existing object or create a new object is to check its documentation. In Kotlin, most of the standard library functions are non-mutating, because Kotlin encourages immutability.

You could try replacing your code with something like:

val groupedAccounts = contentModel.securityAccountList.groupBy { it.currency }

Note how the variable stores the result of the call to groupBy, not the original securityAccountList.