Reversing a string or array in J

rev.j

NB. first attempt, took me a whole hour
sub1 =: 1 & (-~)
subtractindices =: ((# sub1) @: #)
forwardindices =: i. @: #
revindices =: (subindices - forwardindices)
revarray =: (({~) revindices)

NB. alternative implementation, I realised you could give a -ve number to "i."
revindices2 =: (i. @: - @: #) 
revarray2 =: ({~) revindices2

NB. final unreadable version (above but smooshed together)
revarray3 =: ({~) (i. @: - @: #) 

NB. bonus, slightly more readable version using explicit parameters
revarray4 =: 3 : 0
( (((# y) - 1)) - (i. (# y)) ) { y
)