Is ↓[x]Y equivalent to ,/[x]Y for all Y?

Should be. There may be some edge case

↓ is ⊂⍤1 and ,/ on flat data is a no-op along vectors, except that / encloses.

Of course, on nested data they differ

@Adám for aplcart: ⊃∘⊆⍣≡ strip all enclosures

@awagga Doesn't this fail on 'ab' 'cd' or is that intentionally a first?

Oh, yes, I hadn't considered that

You want disclose if scalar?

Yeah

⊃⍤,⍥⊆/⍣≡ works

My other possible meaning for ⊇Y

Or not...

@awagga No, your previous version did.

(⊃,⍥⊆/)⍣≡ is not the same as ⊃⍤,⍥⊆/⍣≡

Yeah, thanks!

You don't want the ⊃ included in the reduction.

Not thinking straight :)

(⊃,⍥⊆/)⍣≡ fails on 'abc'

{⊃,⍥⊆/⊆⍵} is an option then. Not one I like

Note that this will disclose ,⊂X whereas ⍬≡⍴⍵: ⊃⍵ won't

⊃⍣(((0=≡)∨⍬≢⍴)⊣)⊂

{⊃⍣(⍬≡⍴⍵)⊢⍵}⍣≡

> Write a function that takes a vector of vectors as its right argument and returns it sorted by the length of each element.

Note that we'll start 2 hours earlier, beginning next week, 14 October.

This problem should be trivial, and there's probably only one good solution.

I have {⍵[⍋≢¨⍵]}

Using ⍴ instead of ≢ would be a potential pitfall: ⎕←{⍵[⍋⍴¨⍵]} 'one' 2 'three' '' 'four'(5 6 7 8)

@Adám
┌─┬┬───┬────┬───────┬─────┐
│2││one│four│5 6 7 8│three│
└─┴┴───┴────┴───────┴─────┘

This is because lexicographical sorting rules include that "nothing" comes before "something". The shape of a scalar (e.g. 2) is "nothing (⍬) while the shape of an empty vector is "something (,0).

For a generalisation to higher-ranked elements, we could sort by number of elements: {⍵[⍋×/⍤⍴¨⍵]}

And finally, there's shortlex order proper, which I'll leave as an exercise for the reader — or you could just look it up on APLcart ;-)

See you next week for 2016-7: 3s and 5s, but don't forget that it'll be two hours earlier, at 13:00 UTC!

tacit form is a contribution i think...
⊢⌷⍨∘⊂∘⍋≢¨

But really ugly, and same length.

yes :/

With Select as ⊇ and Behind as ⍛, It'll be fine: ≢¨⍋⍛⊇⊢ or (⍋≢¨)⍛⊇

That first expression is a fork with ⍋⍛⊇ as the middle tine right? Took me a moment to spot where the ⍺ Beside needs came from

When is Adam's Friday APL demo?

I remember stumbling on something about it on the APL wiki but I can't find the link again...

Ah, APL Quest, and it was 4 hours ago :sweat-smile: -- I'll try again next week!