title: How to draw a line plot in ggplot using a data.frame file?
body: <p>Thank you for reading. I find that I am unable to draw line plot from my existing data as below:</p>
  
  <pre><code>a=structure(list(ID = structure(1:3, .Names = c("V2", "V3", "V4"
  ), .Label = c(" day1", " day2", " day3"), class = "factor"), 
      Protein1 = structure(c(3L, 1L, 2L), .Names = c("V2", 
      "V3", "V4"), .Label = c("-0.651129553", "-1.613977035", "-1.915631511"
      ), class = "factor"), Protein2 = structure(c(3L, 
      1L, 2L), .Names = c("V2", "V3", "V4"), .Label = c("-1.438858662", 
      "-2.16361761", "-2.427593862"), class = "factor")), .Names = c("ID", 
  "Protein1", "Protein2"), row.names = c("V2", 
  "V3", "V4"), class = "data.frame")
  </code></pre>
  
  <p>What I need is to draw a graph as below:</p>
  
  <p><a href="https://i.stack.imgur.com/eDiDD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/eDiDD.png" alt="enter image description here"></a></p>
  
  <p>I have tried the following codes but the results are not ok;</p>
  
  <pre><code>qplot(ID, Protein1, data=a, colour=ID, geom="line")
  </code></pre>
  
  <p>Also:</p>
  
  <pre><code>a1&lt;-melt(a, id.vars="ID")
  ggplot(a1,aes(ID,value))+ geom_line()+geom_point()
  </code></pre>
  
  <p>So many thanks for your care.</p>