title: Why I get error, when I'm trying to have overlapped density plot using ggplot2?
body: <p>I want to create overlaped density plot. I decided to use ggplot2.</p>
  
  <p>My data are in data frame formate.
  Here How they are look:</p>
  
  <pre><code>Ge&lt;-data.frame(Ge)
  dim(Ge)
  #[1] 100   1
  Ge[1:4,]
  #[1]   6.005409  38.681342 102.079283 185.672611
  dim(Tr)
  #[1] 100   1
  Tr[1:4,]
  #[1] 12.8678547  1.3034715  1.1372413  0.7973491
  </code></pre>
  
  <p>Here is my code to create plot:</p>
  
  <pre><code>library(ggplot2)
  
  ggplot() + geom_density(aes(x=x), colour="red", data=Tr) + 
    geom_density(aes(x=x), colour="blue", data=Ge)
  </code></pre>
  
  <p>But this is the error I get it:</p>
  
  <pre><code>    Don't know how to automatically pick scale for object of type data.frame. Defaulting to continuous
  Error: stat_density requires the following missing aesthetics: x
  </code></pre>
  
  <p>Would someone help me to solve this ?</p>