Actually let me rephrase my question. I hope I am not annoying you with this. I actually put my question wrongly last time.

I actually want (based on the first column) to have the difference of the first and last value (it does not have to be in the same script as you originally wrote, this can be a second script that I would run after running your script that did the magic for me earlier). It outputs the result as follows;

DATA_444_0 299659.88 2686034.50 -5222.89
DATA_444_0 299646.31 2686026.00 -5226.55
DATA_444_0 299634.50 2686018.50 -5229.11
DATA_444_0 299622.41 2686010.75 -5230.46
DATA_451_0 299369.53 2684876.00 -5191.90
DATA_451_0 299357.28 2684869.25 -5194.87
DATA_451_0 299332.78 2684855.50 -5197.94


I want the difference of the last and the 1st value in the last (4th) column for records based on the first column. Thus from the second script (if you can write it as another script) to give me the following result
DATA_444_0 -7.57 # (-5230.46 - ( -5222.8))
DATA_451_0 -6.04 # (-5197.94 - (-5191.0))

............
............


i.e. each time the value changes in the first column, i want the difference of the last and the first record in the 4th column for each value in the first column and output as above.
I hope I am able to describe the question appropriately. I would remember you in my prayers for helping me on this.