title: ggplot: legend label with LaTex expression + variable value + normal text
body: <p>I would like to label a ggplot with a combination of LaTex expression, variable values, and normal text, e.g.</p>
  
  <pre><code>l_decile_names[vec_deciles[1]], " decile (", vec_items[item_current], ")"
  </code></pre>
  
  <p>whereby</p>
  
  <ul>
  <li><code>l_decile_names</code> contains LaTex: <code>"1^{st}", ... "10^{th}"</code></li>
  <li><code>vec_items</code> contains strings <code>"item A", "item B", "item C", ...</code></li>
  </ul>
  
  <p>I can get it to work for a plot title, but not for labels.
  The aim is to plot the legend for the labels below the plot with its content left-aligned.</p>
  
  <p><a href="https://i.stack.imgur.com/UiX7J.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/UiX7J.png" alt="enter image description here"></a></p>
  
  <p>I tried various approaches with <code>bquote()</code>,  <code>expr()</code> and <code>TeX()</code>, e.g.</p>
  
  <pre><code>labels = c("all subjects", 
           TeX(paste0(l_decile_names[vec_deciles[1]], " decile (", vec_items[item_current], ")")),
           TeX(paste0(l_decile_names[vec_deciles[2]], " decile (", vec_items[item_current], ")")))
  </code></pre>
  
  <p>... but without success yet. 
  MWE provided below, help is greatly appreciated!</p>
  
  <pre><code>library(ggplot2)
  library(latex2exp)
  
  vec_deciles &lt;- c(
    1,
    2
    # ...
  )
  l_decile_names &lt;- list(
    '1stDecile' = '1^{st}',
    # ...
    '10thDecile' = '10^{th}'
  )
  
  # survey_items
  vec_items &lt;- c(
    "item A",
    "item B",
    "item C"
    # ...
  )
  item_current &lt;- 3
  
  vec_deciles_label &lt;- paste(l_decile_names[vec_deciles[1]], "and", l_decile_names[vec_deciles[2]])
  
  ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width, color = Species)) +
    geom_boxplot() +
    labs(
      title=TeX((paste0("Scores of ", vec_deciles_label, " decile in ", vec_items[item_current]))),
      x="",
      y="Score"
    ) +
    scale_color_discrete(name = "Scores for ",
      labels = c("all subjects", 
                 "1^{st} decile (item C)",
                 "4^{th} decile (item C)"
  
      )) +
    theme(
          legend.box="vertical",
          legend.position="bottom"
    ) +
    guides(colour=guide_legend(ncol=1, nrow=3, byrow=TRUE))
  </code></pre>