title: column names have periods inserted where there should be spaces
body: <p>In the plot generated by ggplot, each label along the x-axis is a string, i.e., “the product in 1990”. However, the generated plot there is a period in between each word. In other words, the above string is shown as “the.product.in.1990”</p>
  
  <p>How can I ensure the above “.” is not added?</p>
  
  <p>The following code is what I used to add string for each point along the x-axis</p>
  
  <pre><code>last_plot()+scale_x_discrete(limits=ddata$labels$text)
  </code></pre>
  
  <p>Sample code:</p>
  
  <pre><code>library(ggdendro)
  x &lt;- read.csv("test.csv",header=TRUE) 
  d &lt;- as.dist(x,diag=FALSE,upper=FALSE) 
  hc &lt;- hclust(d,"ave") 
  dhc &lt;- as.dendrogram(hc) 
  ddata &lt;- dendro_data(dhc,type="rectangle")
  ggplot(segment(ddata)) + geom_segment(aes(x=x0,y=y0,xend=x1,yend=y1))
  last_plot() + scale_x_discrete(limits=ddata$labels$text)
  </code></pre>
  
  <p>each row of <code>ddata$labels$text</code> is a string, like "the product in 1990".
  I would like to keep the same format in the generated plot rather than "the.product.in.1990" </p>