KProperties API
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.
Last modified: 27 September 2024