mapToColumn

Returns a new DataColumn with the given name and the values that body computes from the rows of this DataFrame.

body is called once for every row, from the first one to the last one, so the new column has one value per row, in row order. The new column is standalone: this DataFrame is not changed and does not contain it.

With an AddExpression, you define the value that each row in the new column should have. This can be based on values from the same row in the original DataFrame.

You can also use functions like prev and next to access other rows, and combine them with newValue to reference values already computed in the new column. For example, use prev().newValue() to access the new column value from the previous row.

See also:

• The Map Operation — an overview of the whole map family.

• add — the same, but the result is this DataFrame with the new column in it.

• map — the same, but the results are collected into a List.

• expr — the same inside the Columns Selection DSL.

Example

// A standalone column of birth years; `df` itself is left as it was
val yearOfBirth = df.mapToColumn("year of birth") { 2021 - age }

For more information: See mapToColumn on the documentation website.

Parameters

import org.jetbrains.kotlinx.dataframe.api.Infer

expr(name, infer, body)

Returns a new DataColumn with the given name and the values that body computes from the rows of this ColumnsContainer.

Use expr instead — it does the same and works in every Columns Selection DSL.