Convert a file of 4-byte cells from little to big endian or vice versa, by directly mapping it into memory and operating on it with sequence words:
USING: alien.c-types grouping io.mmap sequences specialized-arrays ; SPECIALIZED-ARRAY: char "mydata.dat" char [ 4 <groups> [ reverse! drop ] each ] with-mapped-array

Normalize a file containing packed quadruples of floats:
USING: kernel io.mmap math.vectors math.vectors.simd sequences specialized-arrays ; SPECIALIZED-ARRAY: float-4 "mydata.dat" float-4 [ [ normalize ] map! drop ] with-mapped-array