title: ggplot2 each group consists of only one observation
body: <p>I am trying to plot the graph using ggplot2</p>
  
  <p>So I have the following dataframe:</p>
  
  <pre><code>   iter        se perf name
  1    V1 0.6463573 12.8    e
  2    V2 0.3265986 16.8    e
  3    V3 0.2333333 19.1    e
  4    V4 0.1000000 19.9    e
  5    V5 0.0000000 20.0    e
  6    V1 0.7483315 12.6    f
  7    V2 0.6333333 16.3    f
  8    V3 0.6798693 18.8    f
  9    V4 0.2236068 19.5    f
  10   V5 0.1000000 19.9    f
  </code></pre>
  
  <p>and I am trying to plot it in the format similar to this <a href="http://www.cookbook-r.com/Graphs/Plotting_means_and_error_bars_%28ggplot2%29/" rel="noreferrer">page</a> (under Line graphs).</p>
  
  <p>So here is the code for plotting:</p>
  
  <pre><code>pd &lt;- position_dodge(.1)
  ggplot(df, aes(x=iter, y=perf, colour=name)) + 
    geom_errorbar(aes(ymin=perf-se, ymax=perf+se), width=.1, position=pd) +
    geom_line(position=pd) +
    geom_point(position=pd)+
    ylim(0, 20)
  </code></pre>
  
  <p>and it is working nicely: <img src="https://i.stack.imgur.com/9bbft.png" alt="enter image description here">, except that I want these dots to be connected. I tried to add <code>group=1</code> or <code>group=name</code> to this part <code>aes(x=iter, y=perf, colour=name)</code> but it did not help. </p>
  
  <p>I also get these warnings:</p>
  
  <pre><code>ymax not defined: adjusting position using y instead
  ymax not defined: adjusting position using y instead
  geom_path: Each group consist of only one observation. Do you need to adjust the group aesthetic?
  </code></pre>
  
  <p>After looking in the internet, I found that the first two are due to position_dodge, but I think it is because of the ggplot, the third one is actually because of my disconnected points.</p>
  
  <p>Any ideas how to connect them?</p>