Stacking the bars based on attribute variable after equal.count function

Question

I have got three variables; employee, PM and site in my table sitereview. Imported data to R.

 sitereview<-read.csv(file.choose(),header=TRUE)

Sample data pic

Classified data into 6 equal intervals using equal.count function from library(lattice).

 equcount<-equal.count(sitereview$PM,6,0.05)

Plotted this to get the following table.

plot(equcount)

Distribution of PM based on intervals

However, i want these bars to be stacked based on site wise. SOmething like the following pic. Anyway to include attribute variable (site) into these bars.

Looking for bars something like these