title: Merge and Perfectly Align Histogram and Boxplot using ggplot2
body: <p>since yesterday I am reading answers and websites in order to combine and align in one plot an <code>histogram</code> and a <code>boxplot</code> generated using <code>ggplot2</code> package.</p>
  
  <p>This question differs from others because the <code>boxplot chart</code> needs to be reduced in <code>height</code> and <code>aligned</code> to the left outer margin of the <code>histogram</code>.</p>
  
  <p>Considering the following dataset:</p>
  
  <pre><code>my_df &lt;- structure(list(id = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 
  12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 
  28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 
  44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 
  60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 
  76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 
  92, 93, 94, 95, 96, 97, 98, 99, 100), value= c(18, 9, 3, 
  4, 3, 13, 12, 5, 8, 37, 64, 107, 11, 11, 8, 18, 5, 13, 13, 14, 
  11, 11, 9, 14, 11, 14, 12, 10, 11, 10, 5, 3, 8, 11, 12, 11, 7, 
  6, 6, 4, 11, 8, 14, 13, 14, 15, 10, 2, 4, 4, 8, 15, 21, 9, 5, 
  7, 11, 6, 11, 2, 6, 16, 5, 11, 21, 33, 12, 10, 13, 33, 35, 7, 
  7, 9, 2, 21, 32, 19, 9, 8, 3, 26, 37, 5, 6, 10, 18, 5, 70, 48, 
  30, 10, 15, 18, 7, 4, 19, 10, 4, 32)), row.names = c(NA, 100L
  ), class = "data.frame", .Names = c("id", "value"))
  </code></pre>
  
  <p>I generated the boxplot:</p>
  
  <pre><code>require(dplyr)
  require(ggplot2)
  my_df %&gt;% select(value) %&gt;%
          ggplot(aes(x="", y = value)) +
          geom_boxplot(fill = "lightblue", color = "black") + 
          coord_flip() +
          theme_classic() +
          xlab("") +
          theme(axis.text.y=element_blank(),
                axis.ticks.y=element_blank())
  </code></pre>
  
  <p>and I generated the histogram</p>
  
  <pre><code>my_df %&gt;% select(id, value) %&gt;%
          ggplot() +
          geom_histogram(aes(x = value, y = (..count..)/sum(..count..)),
                         position = "identity", binwidth = 1, 
                         fill = "lightblue", color = "black") +
          ylab("Relative Frequency") +
          theme_classic()
  </code></pre>
  
  <p>The result I am looking to obtain is a single plot like:
  <a href="https://i.stack.imgur.com/YTMrk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/YTMrk.png" alt="enter image description here"></a></p>
  
  <p>Note that the boxplot must be <strong>reduced in height</strong> and the <strong>ticks must be exactly aligned</strong> in order to give a different perspective of the same visual.</p>