title: ggplot time series drop date and aligning time axis based on hours
body: <p>I have a data frame with three variables, Name, Heart_rate, Time</p>
  <pre><code>    df  %&gt;%  str
       $ Name     : chr  &quot;A&quot; &quot;A&quot; &quot;A&quot; &quot;A&quot; ...
       $ Heart_rate: num  77 77 77 77 77 77 77 77 77 78 ...
       $ Time      : POSIXct, format: &quot;2021-08-30 06:56:41&quot;
  </code></pre>
  <p>and trying to plot using ggplot.</p>
  <pre><code>    df %&gt;% ggplot(aes(Time, Heart_rate, color=Name)) +geom_line()
  </code></pre>
  <p><a href="https://i.stack.imgur.com/dkiRn.png" rel="nofollow noreferrer">The result is here.</a>
  The problem is those heart rates were measured on different days. I want to plot three person's heart rate time series based only on hours, minutes and seconds, dropping dates(ymd). I tried facet_wrap and scales free option, but the time axis does not match perfectly.</p>
  <pre><code>    df %&gt;% ggplot(aes(Time, Heart_rate, color=Name)) +geom_line() + facet_wrap(~Name,scales=&quot;free_x&quot;, nrow=3) 
  </code></pre>
  <p><a href="https://i.stack.imgur.com/YUHjx.png" rel="nofollow noreferrer">enter image description here</a></p>
  <p>Do you have better ways to do this?</p>