title: Combine ggplots but fix the size/ratio of the plots
body: <p>I have two plots that I combine. <code>arrangeGrob()</code> squeezes them so that the size of the new image is the same as one alone. How can I arrange them while preserving the ratio/size?</p>
  
  <pre><code>require(ggplot2)
  require(gridExtra)
  
  dat &lt;- read.csv("http://www.ats.ucla.edu/stat/data/fish.csv")
  
  frqncy &lt;- as.data.table(table(dat$child))#
  frqncy$V1 &lt;- as.numeric(frqncy$V1)
  
  plot1 &lt;- ggplot(frqncy, aes(x=V1, y= N)) +
      geom_histogram(stat="identity", binwidth = 2.5)
  plot2 &lt;- ggplot(frqncy, aes(x=V1, y= N)) +
      geom_density(stat="identity")
  
  plot &lt;- arrangeGrob(plot1, plot2)
  </code></pre>
  
  <p><code>Plot</code> looks like</p>
  
  <p><img src="https://imgur.com/M8ffUbu.png" alt="Plots become smaller when combined"></p>
  
  <p>I have not found any parameter in <code>ggplot()</code> or <code>arrangeGrob()</code> that fixes the ratio of the input.</p>
  
  <p>Edit: Additional complications arise from the definition of axis labels in <code>arrangeGrob()</code>, i.e.</p>
  
  <pre><code>plot &lt;- arrangeGrob(plot1, plot2, left="LHS label")
  </code></pre>
  
  <p>Then the new file will not automaticall shrink to the minimum height/width combination of <code>plot1</code> and <code>plot2</code>.</p>