Shape each row down to only the selected properties (aliased, when given). dataSet is either a plain array of
rows, or (once groupBy has run) a plain object keyed by group value, each value an array of rows - both are
shaped the same way, row by row.
Shape each row down to only the selected properties (aliased, when given). dataSet is either a plain array of rows, or (once groupBy has run) a plain object keyed by group value, each value an array of rows - both are shaped the same way, row by row.