title: Insert specific unicode symbols inside values of data.frame variable
body: <p>In my data.frame I would like to add two variables, "A" and "B", whose values contain respectively an <strong>n</strong> with the <strong>i</strong> subscript and an <strong>n</strong> with the <strong>s</strong> subscript.<br>
  As I have understood so far, it's not possible to specify an expression for the values of a variable, and hence to add special characters it's necessary to use <strong>unicode symbols</strong>. Some of this unicodes work in R, as for example the greek letter "mu", identified with the unicode <strong>\U00B5</strong>, or numeric subscripts, as you can see in this reprex in your R console:</p>
  
  <pre><code>x &lt;- data.frame("A" = c("\U00B5"),
                  "B" = c("B\U2082"))
  
  print(x)
  </code></pre>
  
  <p>These unicodes work also if I decide to put this variable in a <code>ggplot()</code> object, because I will display the correct symbol ("mu" for example) on the axis text or the facets.<br>
  The problem is that when I do the same for the subscripts of i (unicode: <strong>\U1D62</strong>) and s (unicode: <strong>\u209B</strong>), R doesn't recognise the unicode and prints the whole string inside the variable name.</p>
  
  <p>Do you know how I can resolve this issue and if this unicode works on every operating system?</p>
  
  <p>Thanks</p>