title: Is there a method to set the theta-axis ticks for circular ring plot in ggplot2?
body: <p>I want to show a tick mark for theta axis in the ggplot2 poar plot. However, both axis.ticks.y and axis.ticks.y in the theme() does not work for theta axis. Any help would be appreciated, thanks</p>
  <pre class="lang-r prettyprint-override"><code>library(ggplot2)
  df &lt;- data.frame(
      start = c(0, 121, 241),
      end = c(120, 240, 359),
      group = letters[1:3]
  )
  # a example circular ring plot
  base &lt;- ggplot(df, aes(ymax = end, ymin = start, 
                         xmin = 0.8, xmax = 1, 
                         fill = group)) +
      geom_rect() +
      coord_polar(theta = &quot;y&quot;) +
      xlim(c(0, 1))
  base
  </code></pre>
  <p><img src="https://i.imgur.com/TWsJxDF.png" alt="" /></p>
  <pre class="lang-r prettyprint-override"><code># the tick of y axis can be changed
  base + theme(axis.ticks.y = element_blank(), axis.text.y = element_blank())
  </code></pre>
  <p><img src="https://i.imgur.com/FKKzdYe.png" alt="" /></p>
  <pre class="lang-r prettyprint-override"><code># set the tick of x axis not worked for the theta axis
  base + theme(axis.ticks.x = element_line(color = &quot;black&quot;, size = 2))
  </code></pre>
  <p><img src="https://i.imgur.com/H1XLF8X.png" alt="" /></p>
  <p>Thanks for @Vishal A., the answer from <a href="https://stackoverflow.com/questions/33549739/controlling-ticks-and-odd-text-in-a-pie-chart-generated-from-a-factor-variable-i/33551864#33551864">Controlling ticks and odd text in a pie chart generated from a factor variable in ggplot2</a> used the <code>panel.grid.major.y</code>. However, it will add the major grids rather than ticks like the following:</p>
  <pre class="lang-r prettyprint-override"><code>base + theme(panel.grid.major.y = element_line(colour = &quot;black&quot;))
  </code></pre>
  <p><img src="https://i.imgur.com/3Qcdwlz.png" alt="" /></p>
  <p><sup>Created on 2021-12-20 by the <a href="https://reprex.tidyverse.org" rel="nofollow noreferrer">reprex package</a> (v2.0.1)</sup></p>