title: How to display only integer values on an axis using ggplot2
body: <p>I have the following plot:</p>
  
  <pre><code>library(reshape)
  library(ggplot2)
  library(gridExtra)
  require(ggplot2)
  
  
  
  data2&lt;-structure(list(IR = structure(c(4L, 3L, 2L, 1L, 4L, 3L, 2L, 1L
  ), .Label = c("0.13-0.16", "0.17-0.23", "0.24-0.27", "0.28-1"
  ), class = "factor"), variable = structure(c(1L, 1L, 1L, 1L, 
  2L, 2L, 2L, 2L), .Label = c("Real queens", "Simulated individuals"
  ), class = "factor"), value = c(15L, 11L, 29L, 42L, 0L, 5L, 21L, 
  22L), Legend = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L), .Label = c("Real queens", 
  "Simulated individuals"), class = "factor")), .Names = c("IR", 
  "variable", "value", "Legend"), row.names = c(NA, -8L), class = "data.frame")
  p &lt;- ggplot(data2, aes(x =factor(IR), y = value, fill = Legend, width=.15))
  
  
  data3&lt;-structure(list(IR = structure(c(4L, 3L, 2L, 1L, 4L, 3L, 2L, 1L
  ), .Label = c("0.13-0.16", "0.17-0.23", "0.24-0.27", "0.28-1"
  ), class = "factor"), variable = structure(c(1L, 1L, 1L, 1L, 
  2L, 2L, 2L, 2L), .Label = c("Real queens", "Simulated individuals"
  ), class = "factor"), value = c(2L, 2L, 6L, 10L, 0L, 1L, 4L, 
  4L), Legend = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L), .Label = c("Real queens", 
  "Simulated individuals"), class = "factor")), .Names = c("IR", 
  "variable", "value", "Legend"), row.names = c(NA, -8L), class = "data.frame")
  q&lt;- ggplot(data3, aes(x =factor(IR), y = value, fill = Legend, width=.15))
  
  
  ##the plot##
  q + geom_bar(position='dodge', colour='black') + ylab('Frequency') + xlab('IR')+scale_fill_grey() +theme(axis.text.x=element_text(colour="black"), axis.text.y=element_text(colour="Black"))+ opts(title='', panel.grid.major = theme_blank(),panel.grid.minor = theme_blank(),panel.border = theme_blank(),panel.background = theme_blank(), axis.ticks.x = theme_blank())
  </code></pre>
  
  <p>I want the y-axis to display only integers. Whether this is accomplished through rounding or through a more elegant method isn't really important to me.</p>