+: is double, < is box (which in this example would throw a type error).
Other than that, ... using @. seems to be the way to go.
Thanks,
--
Raul
On Thu, Jul 13, 2023 at 6:01 PM Henry Rich <henryhr...@gmail.com> wrote:
>
> +:`*:@.(1&p:) i. 20 NB. square the primes, double the nonprimes
> 0 2 4 9 8 25 12 49 16 18 20 121 24 169 28 30 32 289 36 361
>
> The rank of the result of the selector verb (1&p:) implies the cell-size
> to be given to the verbs. For large arguments the cells to be fed into
> each verb are collected into an array, so the verb must be able to
> handle such an array of argument cells:
>
> <`*:@.(1&p:) i. 20 NB. square the primes, double the nonprimes
> |rank error, executing monad (<`*:)@.(1&p:)
> |each gerund must return a result whose shape agrees with its inputs
> | <`*:@.(1&p:)i.20
>
> < was passed an array of cells, but it didn't return a result for each cell.
>
> Hey, you did say 'efficiently'.
>
> Henry Rich
>
> On 7/13/2023 5:50 PM, Marcin Żołek wrote:
> > Hello,
> > I need to define a function that will execute function f on the elements of
> > an input array that meet a certain condition, and execute function g on the
> > other elements as in the following code in C. How to do this efficiently in
> > J?
> >
> > for (i = 0; i < N; i++) {
> > if (condition(input[i])) {
> > output[i] = f(input[i]);
> > } else {
> > output[i] = g(input[i]);
> > }
> > }
> >
> > Martin
> > ----------------------------------------------------------------------
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>
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