title: Selecting unique lines based on two columns
body: <p>I've been trying to figure out a way to select lines that are unique based on the values of two columns. For example, here is a sample/example of my file:</p>
  
  <pre><code>chr1    10    12
  chr1    10    12
  chr1    10    11
  chr1    9    12
  chr2    15    20
  </code></pre>
  
  <p>And this is what I want my output to look like:</p>
  
  <pre><code>chr1    10    12
  chr1    10    11
  chr1    9    12
  chr2    15    20
  </code></pre>
  
  <p>I've tried to use this code because I like how it doesn't mess with the order of my file:</p>
  
  <pre><code>awk -F"\t" '!_[$2]++' SNP_positions.txt &gt; SNP_positions_uniq.txt
  </code></pre>
  
  <p>However, it only captures unique features of one column. Is there a way to edit this to make it work for two columns?</p>