To extract a sub-array from an array of real, use extractitem.

set a to createarray 50
set b to extractitem 1 thru 30 step 10 in a blocksize 2
b as list of real
-- {0.0, 1.0, 10.0, 11.0, 20.0, 21.0}

extractitem returns an array of real.

The step and blocksize parameters are optional.