title: How do I plot two grouped (by temperature) dependent variables to a ggplot?
body: <p>Surely there is a simple solution but I cannot figure it out...</p>
  <p>I am trying to plot 2 dependent variables on the sample ggplot plot, grouped by temperature.</p>
  <p>I can plot them both separately but not together.</p>
  <p>I basically want to plot two concentrations of calcium (from differing equations) depending on 4 constant temperatures and pressure.</p>
  <p>FYI:
  Tc = temperature (colour group),
  PCO2 = pressure (x axis),
  Calcium1: concentration using eq 1,
  Calcium2: concentration using eq 2</p>
  <p>My attempted code looks like this:</p>
  <p>(ggplot(data=DCa)</p>
  <ul>
  <li>aes(x=&quot;PCO2&quot;, y=&quot;Calcium1&quot;, color=&quot;Tc&quot;)+ geom_line(aes(group=&quot;Tc&quot;))</li>
  <li>aes(x=&quot;PCO2&quot;, y=&quot;Calcium2&quot;, color=&quot;Tc&quot;)</li>
  <li>geom_line(aes(group=&quot;Tc&quot;))</li>
  <li>ylim(0.0, 2.0)</li>
  <li>labs(x=&quot;PCO$<em>2$ (atm)&quot;, y=&quot;[Ca$^{2+}$]$</em>{app}$ (mmol/L)&quot;, color='T $\degree$C')
  )</li>
  </ul>
  <p>The output is only showing &quot;Calcium2&quot; results.
  <a href="https://i.stack.imgur.com/3u4vS.png" rel="nofollow noreferrer">ggplot output</a></p>
  <p>Does anyone know how to show both concentration groups?</p>