title: What is the difference between rm() and rm(list=ls())?
body: <p>Most of articles, I have read. They recommend to use <code>rm(list=ls())</code> but I do not know what is the difference if I like to use <code>rm()</code></p>
  
  <p>Can I use <code>rm()</code> instead of <code>rm(list=ls())</code> if i would like to clear all variables?</p>
  
  <p>Please give me some advices. Thanks.</p>