R error
Error in .Call.graphics(C_palette2, .Call(C_palette2, NULL)) :
invalid graphics state
reference weblink
https://stackoverflow.com/questions/20155581/persistent-invalid-graphics-state-error-when-using-ggplot2
solution: dev.off()and then running the plot again. I think the graphics device was messed up earlier somehow by exporting some graphics and it didn't get reset. This worked for me and it's simpler than reinstalling ggplot2.运行dev.off()语句，重新运行绘图语句就好了，有点类似于windows的注销操作或清理缓存。