+:`*:@.(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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