title: Align text right justified but center of each box in geom_text
body: <p>I have created a graph with ggplot using geom_tile and geom_text. I want to be able to read the numbers down one column and have them all lineup. I set the font to Courier and used hjust to justify the numbers (otherwise the negative sign throws off the alignment). However I cant find a way to keep this right justification and center the text in the middle each box. Any ideas on how to get the numbers to line up so you can scan a column quickly?</p>
  
  <p>Reproducible example below.</p>
  
  <pre><code>require(reshape2)
  require(ggplot2)
  require(scales)
  
  set.seed(504)
  df_graph &lt;- data.frame("Category"=c("Green","Blue","Red","Yellow","Black","Random1","Random2","Random3","Random4","Random5","Random6","Random7",
                                      "Random8","Random9","Random10"),"Test1"=rnorm(15),"Test1"=rnorm(15),"Test2"=rnorm(15),"Test3"=rnorm(15),
                         "Test4"=rnorm(15),"Test5"=rnorm(15))
  
  df_graph &lt;- melt(df_graph)                       
  df_graph$text &lt;- round(df_graph$value, 2)
  
  colors_used &lt;- c("#B2182B","#D6604D","#F4A582","#FDDBC7","#F7F7F7","#D1E5F0","#92C5DE","#4393C3","#2166AC")
  values &lt;- seq(-4, 4, length = 9)
  
  g &lt;- ggplot(df_graph, aes(variable, Category))
  g &lt;- g + geom_tile(aes(fill = value), colour = "white", size=0.75)
  g &lt;- g + geom_text(aes(label=text),size=3, family="Courier", hjust = 1)
  g &lt;- g + scale_fill_gradientn(colours = colors_used, na.value = "#FFFFFF", values = values,rescaler = function(x, ...) x, oob = identity)
  g &lt;- g + theme_bw()
  g &lt;- g + theme(
    axis.text.x= element_text(color="black", size=10, angle = 45, hjust = 0.5),
    axis.text.y= element_text(color="black", size=8),
    axis.title.y = element_text(color="black",size=10),
    plot.title = element_text(color="black",size=14,face="bold"),
    legend.key = element_rect(fill="white"), legend.background = element_rect(fill=NA),
    legend.position="none",
    legend.title = element_blank(),
    panel.grid  = element_blank(),
    panel.border = element_blank()
  )
  </code></pre>