title: awk - store first occurrence based on cell
body: <p>I have a file (around 10k entries) with following format:</p>
  <pre><code>text1;text2;text3;lat;long
  A;B;C;55.01;12.01
  A;B;C;n/a;n/a
  D;E;F;56.011;13.099
  D;E;F;56.01;13.01
  D;E;F;n/a;n/a
  I;B;C;n/a;n/a
  </code></pre>
  <p>containing duplicates, some without, others with mildly contradicting LAT;LONG coordinates.</p>
  <p>I only want to store first unique value of <code>[$1;$2;$3;$4;$5]</code> as output, so desired output should look like:</p>
  <pre><code>text1;text2;text3;lat;long
  A;B;C;55.01;12.01
  D;E;F;56.011;13.099
  I;B;C;n/a;n/a
  </code></pre>
  <p>I'd assume that I want to create an array, but I struggle with proper formating of it... so any help appreciated !</p>