Column group definitions
column_group.RdCreates a column group definition for grouping columns in a Cheetah Grid widget.
Examples
cheetah(
  iris,
  columns = list(
    Sepal.Length = column_def(name = "Length"),
    Sepal.Width = column_def(name = "Width"),
    Petal.Length = column_def(name = "Length"),
    Petal.Width = column_def(name = "Width")
  ),
  column_group = list(
    column_group(name = "Sepal", columns = c("Sepal.Length", "Sepal.Width")),
    column_group(name = "Petal", columns = c("Petal.Length", "Petal.Width"))
  )
)