title: Combining plots created by R base, lattice, and ggplot2
body: <p>I know how to combine plots created by R graphics. Just do something like</p>
  
  <pre><code>attach(mtcars)
  par(mfrow = c(3,1)) 
  hist(wt)
  hist(mpg)
  hist(disp)
  </code></pre>
  
  <p>However, now I have plots by three different graphic systems</p>
  
  <pre><code># 1
  attach(mtcars)
  boxplot(mpg~cyl,
          xlab = "Number of Cylinders",
          ylab = "Miles per Gallon")
  detach(mtcars)
  
  # 2
  library(lattice)
  attach(mtcars)
  bwplot(~mpg | cyl,
         xlab = "Number of Cylinders",
         ylab = "Miles per Gallon")
  detach(mtcars)
  
  # 3
  library(ggplot2)
  mtcars$cyl &lt;- as.factor(mtcars$cyl)
  qplot(cyl, mpg, data = mtcars, geom = ("boxplot"),
        xlab = "Number of Cylinders",
        ylab = "Miles per Gallon")
  </code></pre>
  
  <p>The <code>par</code> method doesn't work anymore. How can I combine them?</p>