带有facet_grid的ggplot2柱形图

Question

I'm trying to make a R ggplot2 chart with columns grouping one variable, and a facet_grid to break down by another. Both ways I've tried have failed:

1) Setting x as the facet_grid variable breaks down by that variable twice:

ggplot(diamonds, aes(x=cut, y=price, fill=color)) +
    geom_bar(position="dodge", stat="identity") +
    facet_grid(cut ~ ., scales="free")

2) Dropping x produces an error:

ggplot(diamonds, aes(y=price, fill=color)) +
    geom_bar(position="dodge", stat="identity") +
    facet_grid(cut ~ ., scales="free")
# Error in exists(name, envir = env, mode = mode): 
# argument "env" is missing, with no default

Answer 1

Set x to the same variable as the color arg:

ggplot(diamonds, aes(x=color, y=price, fill=color)) +
    geom_bar(position="dodge", stat="identity") +
    facet_grid(cut ~ ., scales="free")