title: ggplot(): Error in FUN(X[[i]], ...) : object not found
body: <p>I wish to do a graph comparing the word use of Trump with Hillary Clinton and Obama in R. For this purpose I have followed the approach from this site:
  <a href="https://www.tidytextmining.com/tidytext.html#word-frequencies" rel="nofollow noreferrer">https://www.tidytextmining.com/tidytext.html#word-frequencies</a></p>
  
  <pre><code>ggplot(frequency, aes(x = proportion, y = `Donald Trump`, color = abs(`Donald Trump` - proportion))) +
    geom_abline(color = "gray40", lty = 2) +
    geom_jitter(alpha = 0.1, size = 2.5, width = 0.3, height = 0.3) +
    geom_text(aes(label = word), check_overlap = TRUE, vjust = 1.5) +
    scale_x_log10(labels = percent_format()) +
    scale_y_log10(labels = percent_format()) +
    scale_color_gradient(limits = c(0, 0.001), low = "darkslategray4", high = "gray75") +
    facet_wrap(~author, ncol = 2) +
    theme(legend.position="none") +
    labs(y = "Donald Trump", x = NULL)
  </code></pre>
  
  <p>My data frame look like this:
  <a href="https://i.stack.imgur.com/RUqZt.png" rel="nofollow noreferrer">enter image description here</a>
  However, I keep getting the error</p>
  
  <pre><code>Error in FUN(X[[i]], ...) : object 'Donald Trump' not found
  </code></pre>
  
  <p>It seems like the error is related to ggplot(). However, I've tried to change this in several ways but I simply can't find the mistake. Hope you can help me out - in advance thanks!</p>