caluclating median distance

[Beema shafreen]

hi everybody,
                    I have a file
10000175    10000234    43    A_16_P03652190
10000277    10000336    387    A_16_P41582022
10000723    10000782    98    A_16_P03652191
10000880    10000932    270    A_16_P41582024
10001202    10001261    539    A_16_P41582025
10001800    10001859    16    A_16_P41582026
10001875    10001923    43    A_16_P21378376
10001966    10002011    361    A_16_P03652193
10002372    10002422    49    A_16_P21378377
10002471    10002527    118    A_16_P03652194
10002645    10002704    187    A_16_P41582029
10002891    10002941    130    A_16_P21378379
10003071    10003121    415    A_16_P03652195
10003536    10003595    -38    A_16_P03652196

how to calculate the median spacing of an data in the file basically
focusing on the third column of an file. say for example the median spacing
is to be 635. how do we programtically calculate the median spacing and sort
the file according to the third column's median spacing.
hope median we calculate  using (N+1)/2

can somebody help me in this point of view

regards
shafreen
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