Enumerations
Factor handbook > The language > Collections

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An enumeration provides a view of a sequence as an assoc mapping integer indices to elements:
enumerated

<enumerated> ( seq -- enumerated )


Inverting a permutation using enumerations:
IN: scratchpad : invert ( perm -- perm' ) <enumerated> sort-values keys ; { 2 0 4 1 3 } invert .
{ 1 3 0 4 2 }