title: Boxplots grouped by group value
body: <p>I have the following example data frame:</p>
  
  <pre><code>Parameter&lt;-c("As","Hg","Pb")
  Loc1&lt;-c("1","10","12")
  Loc2&lt;-c("3","14","9")  
  Loc3&lt;-c("5","12","8")
  Loc4&lt;-c("9","20","6")
  x&lt;-data.frame(Parameter,Loc1,Loc2,Loc3,Loc4)
  x$Loc1&lt;-as.numeric(x$Loc1)
  x$Loc2&lt;-as.numeric(x$Loc2)
  x$Loc3&lt;-as.numeric(x$Loc3)
  x$Loc4&lt;-as.numeric(x$Loc4)
  </code></pre>
  
  <p>The Parameter column holds the names of the heavy metal and Loc1 to Loc4 columns hold the measured value of the heavy metal at the individual location.</p>
  
  <p>I need a plot with one boxplot for each heavy metal at each location. The location is the grouping value. I tried the following:</p>
  
  <pre><code>melt&lt;-melt(x, id=c("Parameter"))
  ggplot(melt)+
    geom_boxplot (aes(x=Parameter, y=value, colour=variable))
  </code></pre>
  
  <p>However, the resulting plot did not somehow grouped the boxplots by location.</p>