library(ggvis)
library(dplyr)
dat <- data.frame(fruit = rep(c("apple", "orange", "banana"), each=2),
                  count = c(20, 40, 30, 70, 40, 50),
                  site = rep(c("site_A", "site_B"), 3))
dat %>% ggvis(~fruit,~count,fill=~site) %>% layer_bars() %>% add_legend("fill",title = "sizeoffruit")