How to select range of bars for calculation

[add.mailme]

Hello,

I am trying to write formula for Hurst Exponent in afl. I am looking out for solution where i need store return data for particular range of period. Lets say we have 100 bars but i want to store return data for bar no. 50 to bar no.75 and then in second array from bar no. 76 to bar no. 100.

Thanks,