title: R - ggplot2 Legend not appearing for line graph
body: <p>I know this question has been asked before, and I've looked at many of the links, but none of them seem to be helping my case.
  I'm plotting a line graph for 4 lines of different colors. But I can't get the legend to appear.</p>
  
  <p>I've read that I need to put the color attribute in the aes part of the graph. That hasn't been successful either.</p>
  
  <p>I have a data frame of four column, and 1000 rows. Here's a small reproducible example of what my data looks like, and how I'd like to plot it.</p>
  
  <pre><code>library(ggplot2)
  
  vec1 &lt;- c(0.1, 0.2, 0.25, 0.12, 0.3, 0.7, 0.41)
  vec2 &lt;- c(0.5, 0.4, 0.3, 0.55, 0.12, 0.12, 0.6)
  vec3 &lt;- c(0.01, 0.02, 0.1, 0.5, 0.14, 0.2, 0.5)
  vec4 &lt;- c(0.08, 0.1, 0.54, 0.5, 0.1, 0.12, 0.3)
  
  df &lt;- data.frame(vec1, vec2, vec3, vec4)
  
  df_plot &lt;- ggplot() +
    geom_line(data = df, color = "black", aes(x = c(1:7), y = df[,1], color = 
  "black")) +
    geom_line(data = df, color = "blue", aes(x = c(1:7), y = df[,2], color = 
  "blue")) +
    geom_line(data = df, color = "green", aes(x = c(1:7), y = df[,3], color = 
  "green")) +
    geom_line(data = df, color = "yellow", aes(x = c(1:7), y = df[,4], color 
  = "yellow")) +
    xlab("x axis") +
    ylab("y axis") +
    ggtitle("A random plot") +
    theme(legend.title = element_text("Four lines"), legend.position = 
  "right")
  </code></pre>
  
  <p>(Also, did SO change the process of indenting code? Before, I could just press Ctrl + K to indent the entire block of code. But I can't do that anymore. Ctrl+K puts the cursor in my URL box for some reason)  </p>
  
  <p>I'd like ti it print the legend to the right of the graph.</p>