@Adám When I tried to run that with the upper bound input (1,000,000) it caused an WS FULL. Is there any way to do something similar for a brute force that wouldn't cause the overflow?

Hi, newbie question. AFAIK this is a fork written out manually, m being a dyadic function and s being an array of strings:

      (2 3 4 m s) ⌿ (2 3 4 ⊢ s)

┌───┬──┬───┐
│abc│de│klm│
└───┴──┴───┘

This does what I expect, finding all strings with length in 2 3 4. However, if I write it as a train, I get an empty array:

      2 3 4 (m ⌿ ⊢) s
┌┐
││
└┘

What's the difference between the two?

For completeness:

s←'abc' 'de' 'fghij' 'klm'
m←{⍺∊⍨,↑⍴¨⍵}
Dyalog APL/S-64 Version 18.2.45405

@Lapwing482 read about hybrids

(also that's a hook!)