convert

Returns DataFrame with changed values in some columns. Allows changing column types.

convert { columnsSelector }
    .with { rowExpression } | .asFrame { frameExpression } | .perRowCol { rowColExpression } | to<Type>() | to { colExpression }

rowExpression = DataRow.(OldValue) -> NewValue
rowColExpression = (DataRow, DataColumn) -> NewValue
colExpression = DataFrame.(DataColumn) -> DataColumn
frameExpression: DataFrame.(DataFrame) -> DataFrame

Related operations: Update / convert values

See column selectors for how to select the columns for this operation and row expressions for how to provide new values.

df.convert { age }.with { it.toDouble() }
df.convert { colsAtAnyDepth().colsOf<String>() }.with { it.toCharArray().toList() }

ColumnGroup can be converted using DataFrame API, for example:

df.convert { name }.asFrame { it.add("fullName") { "$firstName $lastName" } }

Similar to replace with operation, columns can be converted in a compiler plugin-friendly fashion whenever you need to perform an operation on the entire column without changing its name. For example, parallel reading.

df.convert { name }.asColumn { col ->
    col.toList().parallelStream().map { it.toString() }.collect(Collectors.toList()).toColumn()
}

convert {}.to<>() supports automatic type conversions between the following types:

String, Char (uses parse to convert from String to other types)
Boolean
Byte
Short
Int (and Char)
Long
Float
Double (See parsing doubles for String to Double conversion)
BigDecimal
BigInteger
LocalDateTime (kotlinx.datetime and java.time)
LocalDate (kotlinx.datetime and java.time)
LocalTime (kotlinx.datetime and java.time)
Instant (kotlinx.datetime, kotlin.time, and java.time)
enum classes (by name)

If you want to convert Char '1' to the Int 1, use parse() instead, or use String as intermediate type.

df.convert { age }.to<Double>()
df.convert { colsOf<Number>() }.to<String>()
df.convert { name.firstName and name.lastName }.asColumn { col -> col.map { it.length } }
df.convert { weight }.toFloat()

Automatic conversion from String to enum classes is also supported:

enum class Direction { NORTH, SOUTH, WEST, EAST }

dataFrameOf("direction")("NORTH", "WEST")
    .convert("direction").to<Direction>()

And finally, Value classes can be used with convert too. Both as conversion source and target:

@JvmInline 
value class IntClass(val value: Int)

dataFrameOf("value")("1", "2") // note that values are strings; conversion is done automatically
    .convert("value").to<IntClass>()

24 October 2025