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f;.n Sparse Arguments | initial writing: 2000-12-08 last updated: 2004-10-21

The dyad`x f;.n y` now has special code for sparse boolean vector`x` .`` For example:

       ts=: 6!:2 , 7!:2@]

       f0=: {. ; }.                                2-cut case
       f1=: 4 : '(1 (0,x.)}1$.(#y.);0;0) <;.1 y.'  sparse left argument to cut
       f2=: 4 : '(1 (0,x.)}(#y.)$0) <;.1 y.'       dense  left argument to cut

       x=: 1e5
       y=: i.1e6
       x (f0 -: f1) y
    1
       x (f1 -: f2) y
    1
       ts 'x f0 y'
    0.028419 4.72e6
       ts 'x f1 y'
    0.0288414 4.72653e6
       ts 'x f2 y'
    0.0480949 6.82246e6

       p=: ?.20$#y
       p (f1 -: f2) y
    1
       ts 'p f1 y'
    0.0385063 5.95846e6
       ts 'p f2 y'
    0.0635578 8.05395e6

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