r - remove certain legend variables and legend values from ggplot2?

Question

suppose I'm plotting a dataframe in ggplot2 like:

ggplot(iris) + geom_point(aes(x=Sepal.Width, y=Sepal.Length, color=Species, size=Sepal.Length))

two related questions:

1. how can I remove a variable altogether from the legend? For example, still size the points by Sepal.Length but remove Sepal.Length from the legend altogether?

2. how can I remove just a certain value or set of values from the legend? For example, still color the points by Species as above, but in the legend only show the value for setosa and exclude versicolor, virginica?

thanks.

Answer 1

1. As commented by joran, use scale_size(guide = "none").

2. scale_color_discrete(breaks="setosa")