title: adding and removing grid lines from a lattice histogram
body: <p>I have the following code, which creates a histogram:</p>
  
  <pre><code>inst &lt;- data.frame(c(10:27),c(76,97,128,135,137,141,110,94,67,44,39,26,19,12,7,5,2,1))
  names(inst) &lt;- c("instSize","noOfInst")
  library(lattice)
  trellis.par.set(theme = col.whitebg())
  
  myplot &lt;- xyplot(noOfInst ~ instSize, data = inst, 
               type = c("h", "g"), col = "blue",
               xlab = "Instance Size (Number of Aircraft)",
               ylab = "Number Of Instances",
               scales=list(
                 y=list(
                   at=seq(0,150,10),
                   labels=seq(0,150,10) ),
                 x=list(
                   at=seq(10,27,1),
                   labels=seq(10,27,1) )
               )
               )
  </code></pre>
  
  <p>I would like to add the grid lines for every tick in the y axis and remove all of the vertical grid lines. Is that possible?</p>
  
  <p>Thanks</p>