Grouping.kt

data class Grouping(
    val groups: List<Group>,
)

data class Group(
    val standings: List<Standings>,
)

data class Standings(
    val team: Team,
)

data class Team(
    val id: String
)

fun main() {
    val selectedIndex = groupings.indexOfFirst { grouping ->
        grouping.groups.any { group ->
            group.standings.any {
                it.team.id == "4"
            }
        }
    }

    println(selectedIndex)
}

val groupings = listOf(
    Grouping(
        listOf(Group(
            listOf(
                Standings(Team(id = "1")),
                Standings(Team(id = "2")),
            ))
        )
    ),
    Grouping(
        listOf(Group(
            listOf(
                Standings(Team(id = "3")),
                Standings(Team(id = "4")),
            ))
        )
    ),
    Grouping(
        listOf(Group(
            listOf(
                Standings(Team(id = "5")),
                Standings(Team(id = "6")),
            ))
        )
    ),
    Grouping(
        listOf(Group(
            listOf(
                Standings(Team(id = "7")),
                Standings(Team(id = "8")),
            ))
        )
    ),
)

main()