title: Plotting only x and y axis borders (no box) in ggplot2?
body: <p>The convention of some journals is to show only the x and y axis in a plot not a box around the entire plot area.  How can I achieve this in ggplot2?  I tried <code>theme_minimal_cb_L</code> from <a href="https://github.com/hadley/ggplot2/wiki/Themes" rel="nofollow noreferrer">HERE</a> but it seems to erase the entire box around the plot (does not leave the x and y axis) as seen here:</p>
  
  <p><img src="https://i.stack.imgur.com/jaEfJ.png" alt="enter image description here"></p>
  
  <p>Here's the code I'm using:</p>
  
  <pre><code>dat &lt;- structure(list(x = c(0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 
      1.1, 1.15, 1.2, 1.25, 1.3), y1 = c(34, 30, 26, 23, 21, 19, 17, 
      16, 15, 13, 12, 12, 11), y2 = c(45, 39, 34, 31, 28, 25, 23, 21, 
      19, 17, 16, 15, 14)), .Names = c("x", "y1", "y2"), row.names = c(NA, 
      -13L), class = "data.frame")
  
  
  library(reshape2); library(ggplot2)
  dat2 &lt;- melt(dat, id='x')
  
  theme_minimal_cb_L &lt;- function (base_size = 12, base_family = "", ...){
    modifyList (theme_minimal (base_size = base_size, base_family = base_family),
                list (axis.line = element_line (colour = "black")))
  }
  
  ggplot(data=dat2, aes(x=x, y=value, color=variable)) + 
      geom_point(size=3) + geom_line(size=.5) +
      theme_minimal_cb_L()
  </code></pre>