title: Getting the following error despite having variables in suitable format: Error: Invalid input: date_trans works with objects of class Date only
body: <p>I am just trying to plot a small 27 point dataset with X-axis as Date (CommonDate) in date R format, and y-axis as a continuous variable.</p>
  
  <p>Despite having the date variable in Date format, and even after commenting out the part where scale_x_date() is being utilized, I am getting this error. I have tried multiple ways of debugging it based on some of the answers to this particular error, but to no avail.</p>
  
  <p>Sample dataset: I have sample a 12 point dataset out of the 27 point one</p>
  
  <pre><code>    &gt; example
       Brand     Period X2014_2013 X2015_2014 CommonDate Year
  6        B 2014-06-01  -9.168405 -19.508786 2000-05-31 2014
  11       B 2014-11-01  33.747651   0.000000 2000-10-31 2014
  19       B 2014-07-01  50.199601   0.000000 2000-06-30 2014
  20       B 2014-08-01  69.084423   0.000000 2000-07-31 2014
  22       B 2014-10-01 130.377668   0.000000 2000-09-30 2014
  3        B 2014-03-01  29.807692   9.856387 2000-02-29 2014
  NA    &lt;NA&gt;       &lt;NA&gt;         NA         NA       &lt;NA&gt;   NA
  NA.1  &lt;NA&gt;       &lt;NA&gt;         NA         NA       &lt;NA&gt;   NA
  2        B 2014-02-01  21.843116 -13.037997 2000-02-01 2014
  16       B 2014-04-01 601.443299  43.298060 2000-03-31 2014
  5        B 2014-05-01  15.477101 -23.492664 2000-04-30 2014
  23       B 2014-11-01 126.591315   0.000000 2000-10-31 2014
       Month
  6        6
  11      11
  19       7
  20       8
  22      10
  3        3
  NA      NA
  NA.1    NA
  2        2
  16       4
  5        5
  23      11
  </code></pre>
  
  <p>This is the code I am running. Here instead of <code>data = perc_change_YOY_abs</code>, you may use <code>data = example</code></p>
  
  <pre><code>newb_brand_abs_perc_YOY_2015 = 
  ggplot(data = perc_change_YOY_abs, aes(x = CommonDate, y = X2015_2014, colour = Brand))+
  geom_point()+
  geom_line()+
  geom_text(aes(label = paste(round(X2015_2014,0), "%"), hjust = 0, vjust = 1), size = 4)+
  scale_x_date(breaks = date_breaks("months"),labels = date_format("%b"))+
  scale_y_continuous(breaks = pretty_breaks(n = 8))+
  theme_bw()+
  xlab(" ")+
  ylab("%Change 2015 vs. 2014")+
  annotate("text", x = 4, y = 25, label = "Some text")
  
  plot(newb_brand_abs_perc_YOY_2015)
  </code></pre>
  
  <p>Sessioninfo:</p>
  
  <pre><code>&gt; sessionInfo()
  R version 3.2.0 (2015-04-16)
  Platform: x86_64-w64-mingw32/x64 (64-bit)
  Running under: Windows 7 x64 (build 7601) Service Pack 1
  
  locale:
  [1] LC_COLLATE=English_United States.1252 
  [2] LC_CTYPE=English_United States.1252   
  [3] LC_MONETARY=English_United States.1252
  [4] LC_NUMERIC=C                          
  [5] LC_TIME=English_United States.1252    
  
  attached base packages:
  [1] grid      stats     graphics  grDevices utils     datasets 
  [7] methods   base     
  
  other attached packages:
  [1] lubridate_1.3.3 reshape2_1.4.1  plyr_1.8.3     
  [4] gridExtra_0.9.1 scales_0.2.5    lattice_0.20-31
  [7] ggplot2_1.0.1  
  
  loaded via a namespace (and not attached):
   [1] Rcpp_0.11.6      digest_0.6.8     MASS_7.3-40     
   [4] gtable_0.1.2     magrittr_1.5     stringi_0.5-4   
   [7] proto_0.3-10     tools_3.2.0      stringr_1.0.0   
  [10] munsell_0.4.2    colorspace_1.2-6 memoise_0.2.1
  </code></pre>