[R] Loops to produce plots and leyend

[Bea GD]

I've tried several things but I don't manage to get this plot right. Any 
help greatly appreciated!
I'm running a for loop to produce 4 plots at once. Each plot should only 
show data points for a specific group (i.e. 4 plots for groups 1 to 4). 
The coordinates of the points should be petal length and width. The 
colour of these points should codify the species variable. Finally I'd 
like to show a legend for the colours on these plots. It's important 
that each species has a unique colour. Thanks you a lot for your input!

     # Data
     dd <- iris

     dd$group <- ifelse(dd$Sepal.Length>=4.3 & dd$Sepal.Length<5.2, 1,
                          ifelse(dd$Sepal.Length>=5.2 & 
dd$Sepal.Length<6.1, 2,
                                 ifelse(dd$Sepal.Length>=6.1 & 
dd$Sepal.Length<7, 3,
                                        ifelse(dd$Sepal.Length>=7, 4, NA))))
     dd$group <- as.integer(dd$group)

     dd$Species <- c(rep("Wild", 12), rep("Pinky", 12), rep("Orangy", 
12), rep("Smelly", 12),
                     rep("Pretty", 12), rep("Blue", 12), rep("Big", 12), 
rep("Rare", 12),
                     rep("Toxic", 12), rep("Danger", 12), 
rep("Abundant", 18), rep("Last", 12))


     # Code to plot 4 graphs. It doesn't work!
     pdf("plot_test.pdf", width=10, height=10)
     par(mfrow=c(2, 2))
     for(b in unique(dd$group)){
       idx <- dd$group==b
       plot(dd$Petal.Length, dd$Petal.Width, ty="n", 
xlim=range(dd$Petal.Length), ylim=range(dd$Petal.Width))
       cols <- as.numeric(unique(dd$Species))
       points(dd$Petal.Length[idx], dd$Petal.Width[idx],
              col=cols[as.numeric(dd$Species[idx])])
       legend("right", legend=unique(dd$Species[idx]), pch=1, 
col=cols[as.numeric(unique(dd$Species[idx]))])
     }
     dev.off()