title: Selecting the earliest date from a given dataset in R
body: <p>I have a data set with many rows but I picked only a few as shown below and need to pick only the earliest SORT_DT among all with the rest all variables remaining the same. </p>
  
  <pre><code>        CUST_NO ID_NO SYMBOL  AUTO_CREATE_DT     CLASS_TYPE    SORT_DT
  1         107   10120      1    2014-05-12             G/L  2015-01-09
  2         107   10120      1    2014-05-12             G/L  2015-11-10
  3         107   10120      1    2014-05-12             G/L  2014-06-18
  4         107   10120      1    2014-05-12             G/L  2014-05-12
  5         107   10120      1    2014-05-12             G/L  2015-07-10
  6         107   10120      1    2014-05-12             G/L  2015-10-09
  7         107   10120      1    2014-05-12             G/L  2016-04-08
  8         107   10120      1    2014-05-12             G/L  2016-01-08
  9         107   10120      1    2014-05-12             G/L  2016-12-22
  10        107   10120      1    2014-05-12             G/L  2017-01-13
  11        107   10120      1    2014-05-12             G/L  2016-07-08
  12        107   10120      1    2014-05-12             G/L  2017-04-14
  13        107   10120      1    2014-05-12             G/L  2017-04-17
  14        107   10120      1    2014-05-12             G/L  2016-08-31
  15        107   10120      1    2014-05-12             G/L  2015-04-10
  16        107   10120      1    2014-05-12             G/L  2016-12-22
  </code></pre>
  
  <p>I need the output to be in the form of </p>
  
  <pre><code>      CUST_NO   ID_NO      SYMBOL  AUTO_CREATE_DT     CLASS_TYPE    SORT_DT
  1         107     10120      1    2014-05-12             G/L     2014-05-12
  </code></pre>
  
  <p>Please let me know if anyone has a solution for this.</p>
  
  <p>I have also added the new dataset which is</p>
  
  <pre><code>df &lt;- fread("CUST_NO ID_NO SYMBOL  AUTO_CREATE_DT     CLASS_TYPE    SORT_DT
           107   10120      1    2014-05-12             G/L  2015-01-09
          107   10120      1    2014-05-12             G/L  2015-11-10
          107   10120      1    2014-05-12             G/L  2014-06-18
          107   10120      1    2014-05-12             G/L  2014-05-13
          107   10120      1    2014-05-12             G/L  2015-07-10
          107   10120      1    2014-05-12             G/L  2015-10-09
          107   10120      1    2014-05-12             G/L  2016-04-08
          107   10120      1    2014-05-12             G/L  2016-01-08
          107   10120      1    2014-05-12             G/L  2016-12-22
          107   10120      1    2014-05-12             G/L  2017-01-13
          107   10120      1    2014-05-12             G/L  2016-07-08
          108   10120      1    2014-05-12             G/L  2017-04-14
          108   10120      1    2014-05-12             G/L  2017-04-17
          108   10120      1    2014-05-12             G/L  2016-08-31
          108   10120      1    2014-05-12             G/L  2015-04-10
          108   10120      1    2014-05-12             G/L  2016-12-22")
  </code></pre>
  
  <p>The output should be different as below </p>
  
  <pre><code>  CUST_NO   ID_NO      SYMBOL  AUTO_CREATE_DT     CLASS_TYPE    SORT_DT
  1         107     10120      1    2014-05-12             G/L     2014-05-13
  2         108     10120      1    2014-05-12             G/L     2015-04-10    
  </code></pre>