I can label groups in a bar chart but when trying to rotate the column labels I get unexpected results.
This works:
BarChart[{{1, 2, 3}, {4, 5, 6}}, ChartLabels -> {{"c1", "c2"}, {"r1", "r2", "r3"}}] this doesn't:
BarChart[{{1, 2, 3}, {4, 5, 6}}, ChartLabels -> Placed[{{"c1", "c2"}, {"r1", "r2", "r3"}}, Axis, Rotate[#, Pi/4] &]] What am I doing wring?

BarChart[{{1, 2, 3}, {4, 5, 6}}, ChartLabels -> Map[Rotate[#, Pi/4] &, {{"c1", "c2"}, {"r1", "r2", "r3"}}, {2}]]$\endgroup$ChartLabels -> (Placed[#, Axis, Rotate[#, Pi/4] &] & /@ {{"c1", "c2"}, {"r1", "r2", "r3"}})$\endgroup$