title: how to control the line thickness in geom_line
body: <p>I would like to control the thickness for lines in my plotting, however I ran into some difficulty. It seems like if I add <code>size=0.06</code> or <code>size=2</code> in <code>geom_line()</code>, it did not really change the line thickness to different size. Also it added strange legend in the output. how should I fix that?</p>
  <p>I codes I used to do plotting are:</p>
  <pre><code>ggplot(data =df)+
         geom_line(aes(x = ADY, y = AVAL, color = PARAMCD, yaxs=&quot;d&quot;, xaxs=&quot;d&quot;, size=0.06))+
         geom_point(aes(x = ADY, y = AVAL))+
         scale_color_discrete(breaks=c(&quot;SYSBP&quot;, &quot;DIABP&quot;, &quot;PULSE&quot;),name = &quot;Vital signs&quot;, labels = c(&quot;Systolic BP&quot;, &quot;Diastolic BP&quot;,  &quot;Pulse&quot;))+
         scale_colour_manual(values=c(DIABP=&quot;#512d69&quot;,SYSBP=&quot;#007254&quot;,PULSE=&quot;#fd9300&quot;))
  </code></pre>
  <p>The output for <code>size=0.06</code> and <code>size =2</code> are:</p>
  <p><a href="https://i.stack.imgur.com/1Gvx1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1Gvx1.png" alt="enter image description here" /></a></p>
  <p><a href="https://i.stack.imgur.com/cnoun.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cnoun.png" alt="enter image description here" /></a></p>
  <p>Could someone give me some guidance on this? I don't want size to be shown on legend and I would like to control the thickness of the lines.Thanks.</p>
  <p>The sample data can be build using codes:</p>
  <pre><code>df&lt;- structure(list(ADY = c(-6, -6, -6, 1, 1, 1, 8, 8, 8, 15, 15, 
  15, 22, 22, 22, 29, 29, 29, 43, 43, 43, 57, 57, 57, 64, 87, 87, 
  87, 101, 101, 101), AVAL = c(66, 67, 127, 70, 58, 136, 68, 74, 
  140, 145, 74, 58, 75, 72, 149, 82, 66, 143, 86, 60, 159, 64, 
  87, 136, NA, 73, 58, 135, 141, 74, 74), PARAMCD = structure(c(3L, 
  1L, 2L, 1L, 3L, 2L, 3L, 1L, 2L, 2L, 1L, 3L, 1L, 3L, 2L, 1L, 3L, 
  2L, 1L, 3L, 2L, 3L, 1L, 2L, NA, 1L, 3L, 2L, 2L, 1L, 3L), .Label = c(&quot;DIABP&quot;, 
  &quot;SYSBP&quot;, &quot;PULSE&quot;), class = &quot;factor&quot;)), row.names = c(NA, -31L
  ), class = &quot;data.frame&quot;)
  </code></pre>