group
Group columns into ColumnsGroups.
group { columns }
.into(groupName) | .into { groupNameExpression }
groupNameExpression = DataColumn.(DataColumn) -> StringReverse 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()