df-research/dataframe/docs/StardustDocs/topics/group.md

Group columns into ColumnsGroups.

group { columns }
    .into(groupName) | .into { groupNameExpression }

groupNameExpression = DataColumn.(DataColumn) -> String

Reverse operation: ungroup, flatten

It is a special case of move operation.

See column selectors for how to select the columns for this operation.

df.group { age and city }.into("info")

df.group { all() }.into { it.type().toString() }.print()