The problem of removing some data from a large data file

Hi,

I'm trying to reduce a data file by suing some logic. Lets say I have x = 1:1:100 want to define a mid point lets say 50 and then a radius lets say 20km (each unit number from 50 in all directions represents 5km. thats is 51 = 5km away 52 = 10 Km away 49 = 5Km away and son on.

Can anybody help me :)

Thanks

[Geoff Hayes]

Amberly - please describe how your logic fits with your data file. How is your file formatted? What type of data does it contain? How does the 20km fit with your 50? Do you iterate from 30 to 70?

[amberly hadden]

Hi Geoff- I have an earthquake data. A grid file with 30 hundrad thousands values. Now I want to take coordinates (lat lon) of epicentre and use them as a refrence point to define a square or a circle so that points close to epicentre (with in range of lets say 1 dgree) will remain and rest would be deleted out. Thanks

[Geoff Hayes]

Hi Amberly - can you provide a small sample of your data as that might allow someone to provide a solution.