title: Split a data frame based on difference between values in different rows
body: <p>I am not sure I am approaching this in the correct way, but what I am trying to do is split up a data frame into groups based on the difference between values.  For example, using the data below I would like to split on the difference between values in the MIN column, so if the difference is >2 then create a split, in the example below I would end up with 4 split sets of data.</p>
  
  <pre><code>MIN SEC PT  CO2R    CO2D    PAR
  58  10  5   375.7   -11.6   1002
  58  20  5   375.4   -11.6   1001
  58  33  5   375.2   -11.6   1001
  58  43  5   375.2   -11.5   1000
  58  54  5   375.3   -11.8   1000
  2   0   5   375.5   -6.3    1001
  2   8   5   375.3   -6  1000
  2   21  5   375.2   -6.1    997
  2   37  5   375.3   -6.2    993
  2   51  5   375.4   -6.2    1003
  5   20  5   376.3   -7.6    1000
  5   35  5   376.1   -7.3    1000
  5   52  5   375.9   -7.3    1000
  6   5   5   376 -7.8    1000
  6   23  5   376.1   -8  1002
  10  2   5   376.3   -3.3    1003
  10  14  5   376.3   -3.1    1003
  10  27  5   376.5   -3.4    1003
  10  41  5   376.7   -3.7    1006
  10  55  5   376.8   -3.9    997
  </code></pre>
  
  <p>I have used the split function previously when there is unique element to each subset of data, however I have nothing unique in this data set from which to split.  Perhaps this function is not what I need?  Any hints appreciated!</p>
  
  <p>Thanks,</p>