Why this facet_grid doesn't delete columns?

问题:

Hi have this dataset :

tdat=structure(list(Condition = structure(c(1L, 3L, 2L, 1L, 3L, 2L, 
1L, 3L, 2L, 1L, 3L, 2L, 1L, 3L, 2L, 1L, 3L, 2L, 1L, 3L, 2L, 1L, 
3L, 2L, 1L, 3L, 2L), .Label = c("AS", "Dup", "MCH"), class = "factor"), 
    variable = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
    2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 
    3L, 3L, 3L), .Label = c("Bot", "Top", "All"), class = "factor"), 
    value = c(1.782726022, 1, 2.267946449, 1.095240234, 1, 1.103630141, 
    1.392545278, 1, 0.854984833, 4.5163067, 1, 4.649271897, 0.769428018, 
    1, 0.483117123, 0.363854608, 1, 0.195799358, 0.673186975, 
    1, 1.661568993, 1.174998373, 1, 1.095026419, 1.278455823, 
    1, 0.634152231)), .Names = c("Condition", "variable", "value"
), row.names = c(NA, -27L), class = "data.frame")

> head(tdat)
  Condition variable    value
1        AS      Bot 1.782726
2       MCH      Bot 1.000000
3       Dup      Bot 2.267946
4        AS      Bot 1.095240
5       MCH      Bot 1.000000
6       Dup      Bot 1.103630

You can plot it like that using this code :

ggplot(tdat, aes(x=interaction(Condition,variable,drop=TRUE,sep='-'), y=value,
                 fill=Condition)) + 
                 geom_point() +
                 scale_color_discrete(name='interaction levels')+
                                 stat_summary(fun.y='mean', geom='bar',
                 aes(label=signif(..y..,4),x=as.integer(interaction(Condition,variable))))+
                                 facet_grid(.~variable)

But as you can see it doesn't delete unused columns from each facet, do you know why ?

回答1:

You get all levels shown on plot because all levels are used. Levels are dropped if they are not used at all. To remove levels in each facet add scale="free_x" to facet_grid(). But this will not work in particular case because you use different statements of x values in ggplot() and stat_summary() calls. I would suggest to add new column before plotting with interaction.

tdat$int<-with(tdat,interaction(Condition,variable,drop=TRUE,sep='-'))
ggplot(tdat,aes(int,value,fill=Condition))+
  stat_summary(fun.y='mean', geom='bar')+
  geom_point()+
  facet_grid(.~variable,scales="free_x")

In this case you can simplify your code without interaction() because you use also facet_grid().

ggplot(tdat,aes(Condition,value,fill=Condition))+
  stat_summary(fun.y='mean', geom='bar')+
  geom_point()+
  facet_grid(.~variable)