The correct syntax for ggvis is like this:
iris %>% ggvis(~Sepal.Length , ~Sepal.Width, fill= ~Species) %>% layer_points()
See: help(ggvis).
Not this
iris %>% ggvis("Sepal.Length" , "Sepal.Width", fill= "Species") %>% layer_points()
I'm not sure why ggvis() renders a blank plot with the incorrect syntax - perhaps an error message would be better.