title: merging the time stamps of file if label is the same
body: <p>I have file with three columns, the Ist and 2nd column are the start and end of time while the 3rd is label. I want to merge the time stamps of consecutive rows ( 2 or more) if the label in the 3rd column is the same.</p>
  
  <h1>inputs1:</h1>
  
  <p><code>
  0.000000        0.551875        x
  0.551875        0.586875        x
  0.586875        0.676188        t
  0.676188        0.721875        t
  0.721875        0.821250        t
  0.821250        0.872063        p
  0.872063        0.968625        q
  0.968625        1.112250        q
  </code></p>
  
  <h1>inputs2:</h1>
  
  <p><code>
  0.000000        0.551875        x
  0.551875        0.586875        x
  0.586875        0.676188        t
  0.676188        0.721875        t
  0.721875        0.821250        t
  0.821250        0.872063        p
  0.872063        0.968625        q
  0.968625        1.112250        q
  1.112250        1.212250        x
  1.212250        1.500000        x
  </code></p>
  
  <h1>inputs3:</h1>
  
  <p><code>
  0.000000        0.551875        x
  0.551875        0.586875        x
  0.586875        0.676188        t
  0.676188        0.721875        t
  0.721875        0.821250        t
  0.821250        0.872063        oo
  0.872063        0.968625        q
  0.968625        1.112250        q
  1.112250        1.212250        x
  1.212250        1.500000        x
  </code></p>
  
  <h1>output</h1>
  
  <p><code>
  0.000000        0.586875        x
  0.586875        0.821250        t
  0.821250        0.872063        p
  0.872063        1.112250        q
  1.112250        1.500000        x
  </code></p>