title: Offset x axis in ggplot2 bar plot
body: <p>I'd like to create a ggplot2 plot with the bars being on the negative side and the positive side of the x axis like so:</p>
  
  <pre><code>df &lt;- data.frame(
    var1 = c("a", "b", "c", "d", "e", "f", "g"),
    var2 = c(-3, -2, -1, 0, 1, 2, 3)
  )
  
  ggplot(df, aes(x=var1, y=var2, fill=var1)) +
    geom_bar(stat="identity", position="dodge") +
    guides(fill=FALSE)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/BcCjC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BcCjC.png" alt="enter image description here"></a></p>
  
  <p>with the slight difference that the values are all positive. as an example we add 10 to each data point in <code>df$var2</code> and now want to display the relative change around the mean of all values - value 10. the plot should look the same with the exception of the values for the y axis.</p>
  
  <pre><code>df2 &lt;- df
  df2$var2 &lt;- df2$var2 + 10
  </code></pre>
  
  <p>How can I plot df2 to look like df? I don't like to change the labels on the y axis using <code>breaks=</code> and <code>labels=</code> as I have many different plots with ever changing values.</p>
  
  <p>Any help is highly apprechiated!</p>
  
  <p>EDIT:
  To comment on @alistaire 's concerns: I generally agree, nevertheless, I think there are circumstances where such a graph is suited and not necessarily misleading.
  If - for instances - I like to display the relative enrichment or depletion around a mean, but at the same time want to <strong>convey the information what the actual mean is</strong>, than I think such a graph can be quite helpful.</p>
  
  <p>For example: See this figure in Nature Genetics (doi:10.1038/ng.3286)</p>
  
  <p><a href="https://i.stack.imgur.com/kYimM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kYimM.png" alt="enter image description here"></a></p>
  
  <p>Legend(a): <strong>Percentage of fragments</strong> containing GWAS SNPs that interact with a promoter, <strong>segregated by individual disease or trait subclass.</strong> The histogram shows the relative enrichment or depletion of each subclass, as compared to the total catalog of 8,808 SNPs analyzed, with data taken from 1,651 independent studies. The <strong>average association across all SNPs</strong> is shown <strong>as a percentage.</strong></p>