[R] Combining boxplot

[Philippe Massicotte]

Hi everyone.
  
I have two data frames that contain the same variables but with different
number of observation.
  
I would like to know it was possible to combine the data so I can have
"paired" boxplot on the same figure.
  
For example,
  
df1 = data.frame(x = rnorm(100))
df1$type = ifelse(df1$x <= 0 , "type1", "type2")
  
df2 = data.frame(x = rnorm(50,0,2))
df2$type = ifelse(df2$x <= 0 , "type1", "type2")
  
## How to combine boxplot
boxplot(df1$x~df1$type)
boxplot(df2$x~df2$type)
  
df1 would be observed data whereas df2 would be simulated data.
  
I would like to have the two categories (type1 and type2) on x axis and a
colour to differentiate simulated vs observed datra.
  
Regards,
Phil