Emily wanted to know how to do this.
See here for horizontal bars documentation
See here for reversed axis documentation
I couldn’t get $bplot->SetWidth() to work, so used SetAbsWidth
Needed to stagger X axis values so bars didn’t overlap, so first series plotted at 0,2,4,6,8… and second at 1,3,5,7,9…
Once x axis data introduced to new Barplot, seems like rolls reversed, thus this
$bplot1 = new BarPlot($datay1,$datax1);
rather than this
$bplot1 = new BarPlot($datax1,$datay1);