title: Getting this error: Error: Cannot add ggproto objects together. Did you forget to add this object to a ggplot object? when trying to limit display
body: <p>I am working on a project where I am comparing the Legislative Effectiveness Scores (LES) of female house members. I am trying to determine if Democratic female House members are more effective than Republican female House members.
  My data includes the LES for every house member from 1973-2015.
  I am trying to create a plot that ONLY shows female scores, where Democrat points are blue and Republican are Red.</p>
  <p>I found some guidance online but cannot seem to get it to work for my data. Here is what I have been trying.</p>
  <pre><code>pick &lt;- function(condition){
  function(gender) d %&gt;% filter_(Female)
          }
  ggplot(escores, aes(x=Year, y=LES, fill=gender))
  geom_point(size = 4, shape = 4) +
    geom_point(data = pick(~party == &quot;Democrat&quot;), color = &quot;blue&quot;) +
    geom_point(data = pick(~party == &quot;Republican&quot;), color = &quot;red&quot;)    
  </code></pre>
  <p>Any guidance would be appreciated!</p>