R：将data.frame的字符列合并为一个向量

Question

I am working with R and trying to combine two character columns of the data frame into one vector. Let us say, here is my data

a = c("one", "two", "three")
b = c("four", "five", "six")
data = data.frame(a,b)

Now I try

c(data$a, data$b)

or

c(data[,"a"], data[,"b"])

Both give me [1] 1 3 2 2 1 3

What is this?

I would expect and I want the same output as from

c(a,b)

namely [1] "one" "two" "three" "four" "five" "six"

Answer 1

That's because your columns are factors. Convert to characters, and it would work as you expect:

> data[] <- lapply(data, as.character)
> c(data$a, data$b)
[1] "one"   "two"   "three" "four"  "five"  "six"  

Of course, you could always do:

> as.character(unlist(data))
[1] "one"   "two"   "three" "four"  "five"  "six"  

Answer 2

When you're creating your dataframe your vectors are being stored as factors, not characters. You have to specify that you want characters with

 data = data.frame(a,b, stringsAsFactors=F)