How can i creat tow or more plots in one background? I used code: par(mfrow = c(1,2)) can realized it before. but i saw it doesn't work while i using ggplot2. Is there any other way to help me ? i kown some packages that can help me to put the plots together, but i am thinking is there any way to realized it like par(mfrow = c(1,2)) and needn't i write one more code to splice them.