title: remove first two characters for all column names in a data frame in R
body: <p>Is there a way to remove character strings by position from all column names in a data frame</p>
  
  <p>for eg if i have column names like:</p>
  
  <pre><code>ab_sales1 kj_sales2 lm_sales3 .....pk_sales100
  10         34         64      .....  288
  </code></pre>
  
  <p>I would like my output column names to be something like</p>
  
  <pre><code>  sales1 sales2 sales3 .....sales100
      10     34    64     .... 288
  </code></pre>
  
  <p>I know string functions can be used on rows but I could not find something for column names </p>