[R-gui] Sliders and combo Boxes

For the Tk slider and dates, it does not do it directly, but you could set the slider to go across a set of numbers (possibly the Julian date number), suppress the display of the numerical value and instead have a linked label that would show the corresponding date and would update as the slider moves.

The TK combo box does not allow for multiple selection, but the Tk list box does, just set selectmode to either "multiple" or "extended".