对于R中的直方图，x轴上有2个变量

I have a csv file with a couple of variables. Now I am working in R markdown. What I want to do is have a column graph/histogram, where the y-axis is relative frequency, and the x axis is divided into the first variable (x, y, z, ...), and then sub-divided into the next set of variables. I have a csv file with a couple of variables. N