Alternatively If the array is large then } is space efficient
swap =: 4 : '0 0$ ".y,''=:(x{'',y,'')(|.x)}'',y'
list =: 10...@$100
10{.list
59 61 1 92 37 94 26 96 6 2
7!:2'0 4 swap ''list''' NB. space used
4032
10{.list
37 61 1 92 59 94 26 96 6 2
sw=: <@~...@[ C. ]
7!:2' list=: 0 4 sw list'
201327808
Note that the only space efficient form of
such usage of } is y =. x m} y
(http://jsoftware.com/help/dictionary/special.htm)
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