Early days - I haven't studied the Fold family yet, but just applying
your example
worries me a bit if the following is typical:
q =: i. 1000000
ts
6!:2 , 7!:2@]
NB. compare naive (! - ie"old" J) and Fold method to locate match -
might be near end of array:
r[echo ts'r =: 0 *:@[ F:. ([ (1 Z: target&=)) q' [ target =: *:5
NB. near start - better than naive
3.46e_5 6144
0 1 4 9 16 25
r[echo ts'r=:({.~ (target I.~ *: ) ) q' [ target =: *:5
0.0079057 8.3911e6
0 1 2 3 4
10{. r[echo ts'r=:({.~ (target I.~ *: ) ) q' [ target =: *:<:#q
NB. at end - worse than naive!?
0.0153818 8.3911e6
0 1 2 3 4 5 6 7 8 9
10{.r[echo ts'r =: 0 *:@[ F:. ([ (1 Z: target&=)) q' [ target =: *:<:#q
3.54353 8.07812e7
0 1 4 9 16 25 36 49 64 81
I'm thinking of searching a random-ish vector where the match might lie
anywhere.
Thanks,
Mike
On 15/01/2020 21:42, Henry Rich wrote:
0 *:@[ F:. ([ (1 Z: 25&=)) 3 1 4 6 5 7 8 9
9 1 16 36 25
Suggestion for improving Fold are welcomed.
Henry Rich
On 1/15/2020 2:58 PM, 'Sergey Kamenev' via Programming wrote:
Hi!
I need test function f on array x1 x2 ... xn
If f(x) = 0 then no need test another member of array.
I don't understand how write this code loopless.
Main thing: I would avoid of waste computation of f(x) if f(x) = C
found.
I think about Fold but I see only ugly decision with using global
variables.
Example code for rewriting:
NB. Vector with test values
a =: 1 + i. y
f =: *:
example =: monad : 0
for_i. a do.
if. 25 = f i do.
i return.
end.
0
end.
)
example a
Nice day!
Sergey
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