How to combine two columns of factors into one column without changing the factor levels into number [duplicate]

Answer 1

If you factors are inside of data frames then you can combine them this way using rbind:

> df1 <- data.frame(x=factor(c('a','b')))
> df2 <- data.frame(x=factor(c('c','d')))
> rbind(df1,df2)
  x
1 a
2 b
3 c
4 d