title: Plotting geom_point and geom_lines
body: <p>I am trying to make a multilines plot by using <code>ggplot</code>. I also want to plot over the lines some points (which mean the significance). The problem is that when I use <code>geom_point</code>, these points do not coincide with the line that I want. These would be the data:</p>
  
  <pre><code>dat1: 
                  1-4      2-5     3-6      4-7     5-8     6-9    7-10        id
   mod1      -0.035930 0.121970 0.34689 0.034345 0.35312 0.52048 0.58536     mod1
   mod2      -0.094121 0.297150 0.37262 0.512140 0.63918 0.42127 0.73890     mod2
   mod3       0.810550 0.876070 0.57120 0.472640 0.67341 0.79332 0.80882     mod3
   mod4      -0.121970 0.010009 0.49783 0.920100 0.76192 0.45662 0.45526     mod4
  
  dat2:
               1-4     2-5 3-6    4-7     5-8     6-9    7-10        id
   mod1         NaN     NaN NaN    NaN     NaN     NaN     NaN     mod1
   mod2         NaN     NaN NaN    NaN 0.63918     NaN     NaN     mod2
   mod3      0.81055 0.87607 NaN    NaN 0.67341 0.79332 0.80882    mod3
   mod5          NaN     NaN NaN 0.9201 0.76192     NaN     NaN    mod4
  </code></pre>
  
  <p>The plot will contain 4 lines and in the model with some values, I want to plot them with a point.</p>
  
  <p>This is my try:</p>
  
  <pre><code>#Start Plotting
  library(ggplot2)
  library(reshape2)
  dat_r$id &lt;- nam_model  #names of models
  dat_r1$id &lt;- nam_model
  df &lt;- melt(dat_r,id='id')
  df2 &lt;-melt(dat_r1,id='id')
  
  p &lt;-ggplot(df, aes(x=variable,y=value, group=id)) +
       geom_line(aes(color=id), lwd=1) + geom_point(aes(x=df2$variable,y=df2$value,      group=df$id),size = 4)
  </code></pre>
  
  <p>Any suggestion?? I appreciate any idea!</p>
  
  <p>Thanks in advance   </p>