I have a dataset like this:

```
dat<- data.frame(var1= c(1:15), 
                var2= c(rep("A", 4), "control",  rep("B", 4),"control", rep("C", 4), "control"),
                var3= rep(c("full","full", "half", "half", "control"),3),
                value= c(12, 62, 60, 61, 83, 97,1, 22, 99, 47, 63, 49, 25, 81, 26))
dat

```

I for each `level(var3)=="control"` I want to add those rows to each level of `dat$var2`. The result data frame would look like:

```
res<- data.frame(var1= c(1:21), 
             var2= c(rep("A", 7),  rep("B", 7), rep("C", 7)),
             var3= rep(c("full","full", "half", "half", "control","control", "control"),3),
             value= c(12, 62, 60, 61, 83, 47, 26,97,1, 22, 99,83, 47, 26, 63, 49, 25, 81,83, 47,26))

res

```