r - Reduce all columns of data.frame to one long vector -

probably quite basic question, can't seem figure out myself.

i have data.frame this:

 df <- data.frame(x1=1:4,x2=5:8,x3=9:12)

i create 1 long vector columns, that, example, following:

 [1]  1  2  3  4  5  6  7  8  9 10 11 12

how do this?

thanks!

a data.frame special type of list, want, can use:

unlist(df, use.names = false) # [1]  1  2  3  4  5  6  7  8  9 10 11 12

Detect