KProperties API

Edit page Last modified: 14 January 2025

DataFrame can be used as an intermediate structure for data transformation between two data formats. If either source or destination is a Kotlin object, e.g. data class, it is convenient to use its properties for typed data access in DataFrame. This can be done using :: expression that provides property references

data class Passenger(
    val survived: Boolean,
    val home: String,
    val age: Int,
    val lastName: String
)

val passengers = DataFrame.read("titanic.csv")
    .add(Passenger::lastName) { "name"<String>().split(",").last() }
    .dropNulls(Passenger::age)
    .filter {
        it[Passenger::survived] &&
            it[Passenger::home].endsWith("NY") &&
            it[Passenger::age] in 10..20
    }
    .toListOf<Passenger>()

By default, DataFrame uses name and returnType of KProperty for typed access to data. When column name differs from property name, use @ColumnName annotation:

data class Passenger(
    @ColumnName("survived") val isAlive: Boolean,
    @ColumnName("home") val city: String,
    val name: String
)

val passengers = DataFrame.read("titanic.csv")
    .filter { it[Passenger::city].endsWith("NY") }
    .toListOf<Passenger>()

The titanic.csv file could be found here.