title: R plotting mean and standard deviation of simple dataframe without data manipulation
body: <p>I have a simple dataframe <code>data</code></p>
  
  <pre><code>  V1 V2 V3 V4 V5
  1  3  3  3  5  6
  2  3  4  6 10 12
  3  5  6  8 10 11
  4  4  5  7  9 11
  5  2  3  5  8  9
  </code></pre>
  
  <p>This data represents performance during the game for each round. For example in the game 4, a person scored 7 in the third iteration.</p>
  
  <p>And I am trying to create a plot like this (a plot is taken from <a href="http://www.cookbook-r.com/Graphs/Plotting_means_and_error_bars_%28ggplot2%29/" rel="nofollow noreferrer">here</a>):</p>
  
  <p><img src="https://i.stack.imgur.com/5rJID.png" alt="enter image description here"></p>
  
  <p>where on the x axis will rounds and on the y axis the average performance with standard deviation as bars. The average performance is for the first round will be average in the column V1 (3.4), for the second round - 4.2. Standard deviation is also calculated based on V column.</p>
  
  <p>Thanks to BeasterField, I am converting my data in the following way:</p>
  
  <pre><code>df$n &lt;- rownames(df)
  df &lt;- melt(df, id.vars="n", value.name="perf", variable.name="iter" )
  dfc &lt;- ddply(df, .(iter), summarise, se = sd( perf )/sqrt(length(perf)), perf = mean(perf))
  </code></pre>
  
  <p>which gives me the following result:</p>
  
  <pre><code>  iter        se perf
  1   V1 0.5099020  3.4
  2   V2 0.5830952  4.2
  3   V3 0.8602325  5.8
  4   V4 0.9273618  8.4
  5   V5 1.0677078  9.8
  </code></pre>
  
  <p>But later, when I am trying to use ggplot</p>
  
  <pre><code>ggplot(dfc, aes(x=iter, y=perf))+geom_errorbar(aes(ymin=perf-se, ymax=perf+se), width=.1)+geom_line()+geom_point()
  </code></pre>
  
  <p>I receive : <code>geom_path: Each group consist of only one observation. Do you need to adjust the group aesthetic?</code>
  The plot is build without connected lines: <img src="https://i.stack.imgur.com/bPRoR.png" alt="enter image description here"></p>
  
  <p>Also I want my Y axis to have a maximum value of 20.</p>