ggplot geom_tile spacing with facets

Question

I am trying to make a faceted ggplot sorted by two discrete variables on the x axis. The problem is that I would like to have the vertically adjacent entries all touching. Currently there is space between rows based on which levels of the factor are in the top plot vs bottom. sorry this reproducible example is a bit verbose.

npats=20   

simsympt=c(id=1,date=1,tx="control",sympt=0) 

for(i in 1:npats)

 {   days=abs(round(rnorm(1,100,40),0))
     id=rep(as.character(i),days)
     date=1:days
     tx=rep(sample(c("control","treatment"),1),days)
     sympt= sample(0:10, days,p=c(12,3,3,2,1,1,1,1,1,1,1),rep=T)

   simsympt=      rbind(simsympt,      cbind(id,date,tx,sympt) )
  }
       ####tidy things up a bit   
     simsympt=data.frame(simsympt)[-1,]
     colnames(simsympt)=c('id','date','tx','level')
     simsympt$date=as.numeric(as.character(simsympt$date))
     simsympt$level=as.numeric(as.character(simsympt$level))
     #simsympt$id=as.numeric(as.character(simsympt$id))

  head(simsympt)

##now the important stuff

 p <- ggplot(simsympt, aes(x=date,y=id))    
 p=   p + geom_tile(aes(fill=level)) +   
      facet_grid(tx~.,drop=T,space="free")+
      scale_y_discrete(expand=c(0,0),drop=T)
 p

All I need is to remove the all the vertical space between rows in both the top and the bottom graph(facet). For example, since id number 15 is in the control group there should not be a row for her in the treatment group. Thanks, Seth

Answer 1

library("grid")
p + opts(panel.margin=unit(0,"pt"))

EDIT: after further clarification

Removed the wrong space. What you want is to change your facet_grid call to include a scales="free" argument.

p <- ggplot(simsympt, aes(x=date,y=id))    
p=   p + geom_tile(aes(fill=level)) +   
     facet_grid(tx~.,drop=T,space="free",scales="free")+
     scale_y_discrete(expand=c(0,0),drop=T)