title: Plot multiple histogram series in separate charts ggplot2
body: <p>Here's my code:</p>
  
  <pre><code>#set parameters
  p &lt;- 0.41
  n &lt;- 100
  s &lt;- 200
  
  #generate data
  y_1_list = c()
  for (i in 1:s){
    for (j in 1:n){
      vars[j] &lt;- rbinom(1, 1, p)
    }
    y_1_list[i] &lt;- sum(vars) / n
  }
  
  y_2_list = c()
  for (i in 1:s){
    for (j in 1:n){
      vars[j] &lt;- rbinom(1, 1, p)
    }
    y_1 &lt;- sum(vars) / n
    y_2_list[i] &lt;- sum(y_1 - vars)^2 / n
  }
  
  y_3_list = c()
  for (i in 1:s){
    for (j in 1:n){
      vars[j] &lt;- rbinom(1, 1, p)
    }
    y_1 &lt;- sum(vars) / n
    y_3_list[i] &lt;- y_1 / n
  }
  
  y_4_list = c()
  for (i in 1:s){
    for (j in 1:n){
      vars[j] &lt;- rbinom(1, 1, p)
    }
    y_1 &lt;- sum(vars) / n
    y_4_list[i] &lt;- y_1 / sqrt(n)
  }
  
  #bind vectors into data frame
  samples &lt;- data.frame(y_1_list, y_2_list, y_3_list, y_4_list)
  
  #ggplot histograms
  ggplot(data = samples, aes(y_1_list)) + 
    geom_histogram()
  </code></pre>
  
  <p>I'd like to plot four separate histograms, on a 2x2 grid, for each of these series: y_1_list, y_2_list, y_3_list, y_4_list.</p>
  
  <p>The only resources I can find online are for more complicated plots: a) plot data from the same variable split by some other variable b) plot data on the same chart.</p>