title: ggplot2 facet_grid group variables
body: <p>I'm using the following code to create a facet_grid plot:</p>
  
  <pre><code>load(url("http://ebib.com.br/dados.RData"))
  
  library(ggplot2)
  library(scales)
  
  ggplot() + geom_step(data=subset(me, variable=="Umid. Relat."), aes(Data, value), color="blue") +
     geom_smooth(data=subset(me, variable=="Umid. Relat."), aes(Data, value), , color="blue") +
     geom_line(data=subset(me, variable=="Vel. Vento"), aes(Data, value), color="gray20") +
     geom_smooth(data=subset(me, variable=="Vel. Vento"), aes(Data, value), color="gray20") +
     geom_line(data=subset(me, variable==c("Temp. Max.", "Temp. Min.")), aes(Data, value, colour=variable)) +
     geom_smooth(data=subset(me, variable==c("Temp. Max.", "Temp. Min.")), aes(Data, value, colour=variable)) +
     geom_bar(stat="identity", data=subset(me, variable=="Precipitação"), aes(Data, value), fill="blue") +
     facet_grid(variable~., scales="free_y") +
     scale_x_date(breaks = date_breaks("months"), labels = date_format("%b")) +
     theme(legend.position="none")
  </code></pre>
  
  <p>Is there a way to plot the variables "Temp. Max." and "Temp. Min." in the same graph/facet?</p>
  
  <p><strong>Edit: Working code</strong></p>
  
  <pre><code>load(url("http://ebib.com.br/dados.RData"))
  
  library(ggplot2)
  library(scales)
  
  me$variable2 &lt;- as.character(me$variable)
  me$variable2[me$variable2 %in% c("Temp. Max.","Temp. Min.")] &lt;- "Temp. Max./Min."
  
  ggplot() + geom_line(data=subset(me, variable=="Umid. Relat."), aes(Data, value), color="blue") +
  geom_smooth(data=subset(me, variable=="Umid. Relat."), aes(Data, value), , color="blue") +
  geom_line(data=subset(me, variable=="Vel. Vento"), aes(Data, value), color="gray20") +
  geom_smooth(data=subset(me, variable=="Vel. Vento"), aes(Data, value), color="gray20") +
  geom_line(data=subset(me, variable==c("Temp. Max.", "Temp. Min.")), aes(Data, value, colour=variable)) +
  geom_smooth(data=subset(me, variable==c("Temp. Max.", "Temp. Min.")), aes(Data, value, colour=variable)) +
  geom_bar(stat="identity", data=subset(me, variable=="Precipitação"), aes(Data, value), fill="blue") +
  facet_grid(variable2~., scales="free_y") +
  scale_x_date(breaks = date_breaks("months"), labels = date_format("%b")) +
  theme(legend.position="none")
  </code></pre>