title: How to remove + (plus sign) from string in R?
body: <p>Say I use gsub and want to remove  the following (=,+,-) sign from the string and replace with an underscore. </p>
  
  <p>Can someone describe what is going on when I try to use the gsub with a plus sign (+).  </p>
  
  <pre><code>test&lt;- "sandwich=bread-mustard+ketchup"
  # [1] "sandwich=bread-mustard+ketchup"
  
  test&lt;-gsub("-","_",test)
  # [1] "sandwich=bread_mustard+ketchup"
  
  test&lt;-gsub("=","_",test)
  # [1] "sandwich_bread_mustard+ketchup"
  
  test&lt;-gsub("+","_",test)
  #[1] "_s_a_n_d_w_i_c_h___b_r_e_a_d___m_u_s_t_a_r_d_+_k_e_t_c_h_u_p_"
  </code></pre>