[R] Getting rid of rows matching a certain condition

[arun]

HI,
Please check this link (http://r.789695.n4.nabble.com/Remove-levels-td4669441.html).  It was posted today.
df1<-subset(df, Trt!="blank") 
df2<- df1
df1$Trt<- factor(df1$Trt)
levels(df1$Trt)
#[1] "Trt1" "Trt2"


#or
 df2$Trt<-droplevels(df2$Trt)
 levels(df2$Trt)
#[1] "Trt1" "Trt2"
A.K.



Hey guys 
I am new and a beginner. So far I searched the forum for an answer. Did not found anything. 
Here is the Problem. 

I have a data.frame 



Time <- c(1,2,1,1,2,2,3,3)                       
Trt <- factor(c("blank", "blank", "Trt1", "Trt1", "Trt1", "Trt2", "Trt2", "Trt2")) 
OD600 <- c(0.1,0.2,0.18,0.3,0.16,0.21,0.25,0.16) 
df <- data.frame(Time,Trt,OD600) 

No I apply: 

df<-subset(df, Trt!="blank") 
  
So the data.frame has no rows matching Trt=blank" anymore (looking at the data set). So far so good. 

However if I type in: 
levels(df$Trt) 
I get the result: [1] "blank" "Trt1"  "Trt2" 

Somehow it is still somwhere. How can I remove the blank from the data.frame definitely? 

Thanks for the help.