r - rbind char vector to data frame

Question

> test <- data.frame()
> test<-rbind(test,c("hi","i","am","bob"))
> test<-rbind(test,c("hi","i","am","alice"))
Warning message:
In `[<-.factor`(`*tmp*`, ri, value = "alice") :
  invalid factor level, NAs generated

Why does this minimal example produce that error? I want to append several string-rows to an empty data frame.

Answer 1

You can store your information in a character matrix. Of course, you can convert this matrix into a data frame using as.data.frame and the argument stringsAsFactors = FALSE.

> test <- matrix(c("hi","i","am","bob"), nrow = 1)
> test <- rbind(test, c("hi","i","am","alice"))
> test
     [,1] [,2] [,3] [,4]   
[1,] "hi" "i"  "am" "bob"  
[2,] "hi" "i"  "am" "alice"

> testDF <- as.data.frame(test, stringsAsFactors = FALSE)
> testDF <- rbind(testDF, c("hi","i","am","happy"))
> testDF
  V1 V2 V3    V4
1 hi  i am   bob
2 hi  i am alice
3 hi  i am happy