Join columns of the same data.frame in rstudio : How to join 2 columns in rstudio from a single data.frame

For example: 

Column A : a,b,c,d,e
Column B : b,c,a,b,e

The column i want

New Column : a,b,c,d,e,b,c,a,b,e

Basically i want to get all data under both columns into a single column using rstudio