title: How do I create objects to insert in ggplot (when there are multiple parts with +)?
body: <p>In my analysis work I use <code>ggplot</code> in <code>R</code> to produce multiple plots.  I would like to set my desired plot theme (using <code>ggtheme</code> plus some manual changes) as a single object and then call this theme in each of the plots I produce.  I have given an example below.</p>
  <p>This code throws an error due to the presence of the <code>+</code> in the definition of my theme object.  The <code>ggplot</code> function recognises this symbol as adding new elements, but I am not able to use this symbol when creating a separate <code>THEME</code> object to call in <code>ggplot</code>.  Obviously I could transfer the main theme into the <code>ggplot</code> call and just keep my manual changes in <code>THEME</code>, but I would like to have the whole thing in one object for brevity.</p>
  <pre><code>#Load libraries
  library(ggplot2)
  library(ggthemes)
  
  #Create mock data for illustrative purposes
  DATA &lt;- data.frame(x = c(3,6,8,11,2,7,4,4,3,6),
                     y = c(12,8,8,4,15,10,9,13,11,6))
  
  #Set theme for plots
  THEME &lt;- theme_economist() + scale_colour_economist() +
           theme(plot.title    = element_text(hjust = 0.5),
                 plot.subtitle = element_text(hjust = 0.5, face = 'bold'),
                 axis.title.y  = element_text(face = 'bold', size = 12),
                 plot.margin        = margin(t = 0, r = 20, b = 0))
  
  #Error: Don't know how to add RHS to a theme object
  
  #Generate plot using above theme
  FIGURE &lt;- ggplot(data = DATA, aes(x = x, y = y)) +
            geom_point() + THEME
  FIGURE
  </code></pre>
  <p><strong>Question:</strong> How do I amend my definition of <code>THEME</code> to allow me to specify my theme and changes in a single object that can be called later in <code>ggplot</code>?</p>