dataframe - Data.frame in R: concatenation of two column, numbers instead of occurrences -

i have simple question, cannot find answer: have data.frame:

b=c("a","a","a","a","a","b","b","b","b","c") c=c("b","b","b","b","b","c","c","c","c","d")  a<-data.frame(b,c) 

why if i'd put in 1 column a$b , a$c vector this:

f<-c(a$b,a$c) 

the result not like

> f<-c(b,c) > f  [1] "a" "a" "a" "a" "a" "b" "b" "b" "b" "c" "b" "b" "b" "b" "b" "c" "c" "c" "c" "d" 

but

> f<-c(a$b,a$c) > f  [1] 1 1 1 1 1 2 2 2 2 3 1 1 1 1 1 2 2 2 2 3 

? in advance!

edit: tried this, looking @ possible duplicate suggest above:

> a<-data.frame(z=as.character(b),k=as.character(c)) > f<-c(a$z,a$k) > f  [1] 1 1 1 1 1 2 2 2 2 3 1 1 1 1 1 2 2 2 2 3 

you have set stringsasfactors false in data.frame() function. otherwise strings interpreted factors, resulting in undesired output.

b <- c("a","a","a","a","a","b","b","b","b","c") c <- c("b","b","b","b","b","c","c","c","c","d")  <- data.frame(b,c, stringsasfactors = f)  f <- c(a$b,a$c)  f [1] "a" "a" "a" "a" "a" "b" "b" "b" "b" "c" "b" "b" "b" "b" "b" "c" "c" "c" "c" "d"