FWIW: A variant for domodify (no improvement in speed though):
domodify=: ,:^:(1 = #...@$)@] , (modify {:^:(1 ~: #...@$))
data=: (1e3 10 10 $ i.100),"1 0 (10*1+i.1e3)
3{0{data
30 31 32 33 34 35 36 37 38 39 10
ts 'it=:([: }:"1 domodify/@|.)"2 data'
0.145372 1056832
3{0{it
1230 2341 3452 4563 5674 6785 7896 9007 10118 11229
--
Met vriendelijke groet,
=@@i
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