@EriktheOutgolfer
Rebuilding user command cache... done
Was OFF -fns=off
⍎DOMAIN ERROR
__field_initialize_result_←(⎕NS ⍬).⍎'⎕CY''salt''⋄⎕SE.UCMD''box on -fns=on''⊣enableSALT' ⋄ ⎕←(⊂1 3)2⊃2 3⍴(1 2)(3 4)(5 6)(7 8)(9 10)(11 12)
∧
Real time: 1.015 s
User time: 0.930 s
Sys. time: 0.041 s
CPU share: 95.65 %
Exit code: 0
@RosLuP Also, to write rho (⍴) use the linked language bar on the right (second pinned message), or copy from the list of characters (third pinned).
@RosLuP Even though ¨ would make a list of enclosed items, since the items here are simple scalars, they cannot be enclosed, and thus fuse into a simple vector.
Dyadic ⊆ is also called partition (⊂ and ⊆ originate with different APL dialects, but Dyalog APL now features both). To distinguish them, we can call ⊂ "partitioned enclose" and ⊆ just "partition", but it doesn't say much.
@RosLuP What you want to look at is the depth, not the rank:
The first one has an additional layer of nesting (="deeper depth").
@RosLuP Both of them are two element vectors, however. The first is a vector of vectors, the second a vector of scalars.
Dyadic ⊆ works similarly to dyadic ⊂ but with different rules for the left argument. The left argument is non-negative integer instead of Boolean, and new partitions begin whenever an element is higher than its neighbour on the left. Also, elements indicated by 0s are dropped completely:
@EriktheOutgolfer You can evaluate an APL expression by typing it into chat prefixed by ⍞←. Use ⎕← instead for boxed display and multi-line results. Do not use markdown. Commands: )lb for language bar, )help for table of language elements, )docs for full documentation, )ref for PDF reference card.
@EriktheOutgolfer Yes, which means that in most cases you can count ⊆ as a single byte, even though it isn't in the character set. However, then you can't use ⊂, and monadic ≡ becomes less powerful.
Monadic ⌷ is almost the same as monadic⊢ (i.e. identity). However, it will "materialise" the default property of a class. For collections, this means the Item property, so in effect it turns collections into vectors of items.
Dyadic ⌷ is similar to dyadic ⊃ but works its way into the rank instead of the depth. On a 3D array, the first element selects layer, the second row, the third column:
@Adám
Rebuilding user command cache... done
Was OFF -fns=off
⍎INDEX ERROR
__field_initialize_result_←(⎕NS ⍬).⍎'⎕CY''salt''⋄⎕SE.UCMD''box on -fns=on''⊣enableSALT' ⋄ ⎕←(⊂1 3)⌷2 3 4⍴⎕A
∧
Real time: 1.070 s
User time: 0.918 s
Sys. time: 0.077 s
CPU share: 92.99 %
Exit code: 0
@EriktheOutgolfer I think we are holding at a good spot, having covered the array-packaging and array-unpackaging functions. Next up are the unrelated grades.
@EriktheOutgolfer ⍳ and / and ⍴ form the core of most applications. Interesting, isn't it, that we added a new primitive in 16.0 which encapsulates exactly those three? ⍸ is essentially {⍵/⍳⍴⍵}.
@EriktheOutgolfer In fact, the interpreter recognises the sequence /⍳⍴ and tokenises it as a single token. It then evaluates it in an optimised manner, increasing speed and reducing memory usage compared to performing each of the three operations separately.
@EriktheOutgolfer When you fix (i.e define) a function, the interpreter tokenises your code so that it will run without interpretive overhead. It recognises certain multi-primitive patterns at tokenisation time and makes them into single tokens that are different from the single-primitive tokens.
@EriktheOutgolfer Well, we did add ⍸, but there are so many patterns. You wouldn't want a symbol for each one. Part of the power of (Dyalog) APL is exactly that you can express yourself in a relatively simple language, and then have very optimised C code actually do the computation – all without you having to worry about which special arguments' case you have this time around.
@EriktheOutgolfer There are also many function compositions and dfn snippets that are recognised in certain contexts or with certain arguments, and run special dedicated code.
@Uriel Yes. But that only applies to simple arrays. ⌷ can never dig into the scalars of an array. ⊃ can never return multiple elements from different locations.
