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11:22 AM
Christmas came a bit early at #Dyalog ... new toys and an APL joke! 4⍴○3 new build #raspberrypi running on @BitScopeDesigns blade
 
 
1 hour later…
12:27 PM
@Adám what do I need to put in tio header to show box display?
I tried the things you sent to tio bot and they failed
 
@Adám oh, apparentaly I put io←0 before that code, rather then after, and that's why it failed
 
@Adám hmm I would expect core functions to save io on entry and restore on exit when specific one needed (no critisism intended, it just might cause bugs for real world users)
 
@Uriel Utility functions, yes. Functions from the dfns workspace handle ⎕IO variations, but enableSALT was never intended to be run like that. Usually SALT is enabled at start-up. However, TIO runs a bare-bones system for performance.
 
12:59 PM
@Feeds what, why pi * 3, pi * 3, pi * 3, pi * 3?
how is that related to christmas, hmm
 
1:27 PM
@EriktheOutgolfer We got four (Raspberry) Pi 3s (as "presents").
 
 
1 hour later…
2:50 PM
Adám is hosting another informal APL learning session tonight at 18:30 UTC in https://chat.stackexchange.com/rooms/52405/apl , continuing the previous week's "APL primitive functions' marathon". See https://chat.stackexchange.com/transcript/message/41299896#41299896 … if you don't have 20 Stack Exchange rep points.
 
 
4 hours later…
6:30 PM
Welcome to the APL learning session!
We're in the middle of our functions' marathon. Next up is , called "Grade".
 
First time here, any quick notes on what I should know in terms of prior knowledge to the language or classroom etiquette?
 
Note that you can follow the second link on the right to install a language bar, and key bindings so that you can easily type APL characters.
@HyperNeutrino You can find previous lessons here. Only really lesson 1 is necessary.
 
Ah okay, thanks!
 
Please feel free to interrupt with any questions.
Monadic takes a simple (non-nested) array and returns the indices of the major cells reordered so that they would order the array.
Easiest to understand with an example:
⍞←⍋3 1 4 1 5
 
@Adám 2 4 1 3 5
 
6:37 PM
This means that the second element (1) is the smallest, then the fourth (1), then the first (3), etc.
So, we can use this to sort the array:
⍞←3 1 4 1 5[⍋3 1 4 1 5]
 
@Adám 1 1 3 4 5
 
so grade(a)=b means that a[x] for x in b is the same as sorted(a)?
 
@HyperNeutrino Exactly. Also, use the language bar so you can have proper APL characters.
 
ooh ok I'll install that right now
oh this is equivalent to jelly :D
 
@HyperNeutrino However, you don't need the loop (for x in b) as APL allows indexing with an array, and the result has the same shape as the indexing array.
 
6:39 PM
ah ok I see how this works
 
@HyperNeutrino Well, I bet the U stands for "Grade Up". Jelly comes from J which comes from APL.
 
Yeah. That seems to make the most sense.
 
It works on high-rank arrays too:
⎕←3 2⍴2 7 1 8 2 8
 
@Adám
2 7
1 8
2 8
 
⎕←⍋3 2⍴2 7 1 8 2 8
 
6:41 PM
@Adám
2 1 3
 
So the first is row 2 (1 8) then row 1 (2 7) then row 3 (2 8).
 
so the ordering of the arrays is lexicographical or something?
 
@HyperNeutrino Yes.
 
Works on characters too, where it grades in Unicode point order:
⎕←5 2⍴'HelloWorld'
 
6:42 PM
@Adám
He
ll
oW
or
ld
 
⎕←⍋5 2⍴'HelloWorld'
 
@Adám
1 5 2 3 4
 
⎕←(5 2⍴'HelloWorld')[⍋5 2⍴'HelloWorld';]
 
@Adám
He
ld
ll
oW
or
 
⎕←2 2 2⍴⍳8
 
6:44 PM
@HyperNeutrino
1 2
3 4

5 6
7 8
 
⎕←⍋222⍴⍳8
 
@HyperNeutrino
1 9 17 25 33 41 49 57 65 73 81 89 97 105 113 121 129 137 145 153 161 169 177 185 193 201 209 217 2 10 18 26 34 42 50 58 66 74 82 90 98 106 114 122 130 138 146 154 162 170 178 186 194 202 210 218 3 11 19 27 35 43 51 59 67 75 83 91 99 107 115 123 131 139 147 155 163 171 179 187 195 203 211 219 4 12 20 28 36 44 52 60 68 76 84 92 100 108 116 124 132 140 148 156 164 172 180 188 196 204 212 220 5 13 21 29 37 45 53 61 69 77 85 93 101 109 117 125 133 141 149 157 165 173 181 189 197 205 213 221 6 14 22 30 38 46 54 62 70 78 86 94 102 110 118 126 134 142 150 158 166 174 182 190 198 206 
 
no wait
⎕←⍋2 2 2⍴⍳8
 
@HyperNeutrino
1 2
 
@HyperNeutrino First layer, second layer.
 
6:45 PM
Did I do something wrong?
wait nvm
 
@HyperNeutrino No, that's right.
 
oh right. that makes sense thanks
 
⎕←4 2 2⍴'Hello World PPCG'
 
@Adám
He
ll

o
Wo

rl
d

PP
CG
 
⎕←⍋4 2 2⍴'Hello World PPCG'
 
6:46 PM
@Adám
1 4 2 3
 
Layer 1, layer 4, layer 2, layer 3.
⎕←{⍵[⍋⍵;]}4 2 2⍴'Hello World PPCG'
 
@Adám

Rebuilding user command cache... done
Was OFF -trains=box -fns=off
⍎RANK ERROR
 __field_initialize_result_←(⎕NS ⍬).⍎'⎕CY''salt''⋄⎕SE.UCMD''box on -fns=on -trains=tree''⊣enableSALT' ⋄ ⎕←{⍵[⍋⍵;]}4 2 2⍴'Hello World PPCG'
                                                                                                        ∧

Real time: 1.177 s
User time: 1.069 s
Sys. time: 0.046 s
CPU share: 94.81 %
Exit code: 0
 
how do you type backticks
 
@HyperNeutrino backtick,space
⎕←{⍵[⍋⍵;;]}4 2 2⍴'Hello World PPCG'
 
@Adám
He
ll

PP
CG

o
Wo

rl
d
 
6:47 PM
:D cool thanks! also tab backtick seems to work for some reason (I accidentally found that out lol :P)
 
@HyperNeutrino Interesting, unintentional, useful.
@all Anything else about monadic ?
 
⎕←⍋⍋4 2 5 1 3
 
@HyperNeutrino
4 2 5 1 3
 
⎕←⍋4 2 5 1 3
 
@HyperNeutrino Cardinal numbers.
 
6:49 PM
?
 
⎕←⎕←3
 
@HyperNeutrino ⍋⍋ is the cardinal numbers:
 
@RosLuP
3
3
 
oh lol
 
⍞←⍋'PPCG'
 
6:50 PM
@Adám 3 4 1 2
 
⍞←⍋⍋'PPCG'
@DyalogAPL Hello?
⍞←⍋⍋'PPCG'
 
@Adám 3 4 1 2
 
what's the difference between ⍞ and ⎕?
I don't quite understand cardinal numbers..
 
So P is the third, P is the fourth, C is the first, and G is the second.
 
@Adám hello, had to study...
 
6:52 PM
@HyperNeutrino ⍞← makes an inline response of the first line of the output, and without box drawing characters. ⎕← makes a multi-line response with boxed display.
 
@Adám I thought those were ordinals? Or are you referring to what they return as ordinals?
 
ooh okay, thanks!
 
⎕←⍋2 2 2, 4 5 6
 
@RosLuP
1 2 3 4 5 6
 
@RosLuP (2 2 2) (4 5 6)?
 
6:53 PM
@RosLuP 2 2 2, 4 5 6 is the same as 2 2 2 4 5 6
 
⎕←⍋ ⍋ 4 2 5 1 3
 
@HyperNeutrino
4 2 5 1 3
 
@Adám wait huh
 
@RosLuP ⎕←2 3⍴2 2 2, 4 5 6
 
does putting a space between the two ⍋ help?
 
6:53 PM
how does grade up multiple times return cardinal numbers...I thought it was just the same as grade up once
 
@HyperNeutrino Between what?
@EriktheOutgolfer It is so that the grade of the grade is the cardinal numbers. That is in the nature of grading.
 
oh I think I get why. grading my test list returns the list itself :P
⎕←⍋ ⍋ 3 5 4 1 2
 
@HyperNeutrino
3 5 4 1 2
 
@HyperNeutrino Yes, if your numbers are all the integers from 1 to n.
 
my numbers were 4 2 5 1 3
 
6:55 PM
@HyperNeutrino Because 3 is the third, and 5 the fifth.
 
yeah :P
 
So grade grade returns the numbers fitted to 1 ... length(list)?
 
it was a product of distinct swaps
 
@Adám um how does ⍋⍋ differ from just
 
if you continue applying ⍋ multiple times eventually it will form a cycle. I wonder if the period of the cycle has anything to do with the original list
 
6:56 PM
@Zacharý So applying to a permutation inverts it (swaps between cardinal and grade)
 
⎕←2 3⍴2 2 2, 4 5 6
 
@RosLuP
2 2 2
4 5 6
 
@HyperNeutrino The period is 2.
 
oh
well then :P
)about
 
@HyperNeutrino 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.
 
6:57 PM
that's an interesting command syntax for a chatbot :P the unmatched parentheses are bugging me :P
 
@EriktheOutgolfer is the indices of cells in the order that would sort them. ⍋⍋ is the position each will take when sorted. If you think about it hard, you'll see what swaps back and fort between these two.
 
@HyperNeutrino That's APL
 
@HyperNeutrino In APL, all non-syntactic system commands begin with )
 
ooh okay, interesting
 
@Adám oh so it's the same, but different explanation?
 
6:59 PM
@HyperNeutrino It clearly tells the system that this line is not an APL statement.
 
⎕←2 3⍴2 2 2 4 5 6
 
@RosLuP
2 2 2
4 5 6
 
cool ok
 
@EriktheOutgolfer No. they are different ways to state how an array is ordered.
 
@Adám can you please give an example where they are different? everything I've ever tried it on makes it look like they're equivalent...
 
7:01 PM
⎕←⍋'random' ⋄ ⎕←⍋⍋'random'
 
@Adám
2 4 6 3 5 1
6 1 4 2 5 3
 
so ⍋ once is what order the elements would be in when sorted and ⍋ twice is the indices that each element would go to?
 
@EriktheOutgolfer ^ Column 1 says: the "lowest" letter is number two (a) while r is the sixth.
@HyperNeutrino Exactly. Bravo!
 
7:03 PM
⎕←⍋'aedcb'⋄⎕←⍋⍋'aedcb'
 
@EriktheOutgolfer
1 5 4 3 2
 
⍋⍋⍋ is equivalent to , right?
 
⎕←⍋'aedcb'⋄⎕←⍋⍋'aedcb'
 
@EriktheOutgolfer
1 5 4 3 2
1 5 4 3 2
 
7:04 PM
@Zacharý Yes.
 
⎕←⍋'edcba' ⋄ ⎕←⍋⍋'edcba'
 
lol if the input list can be represented as a product of disjoint 2-cycles applied to its sorted version then ⍋ and ⍋⍋ do the same thing xD
 
@EriktheOutgolfer
5 4 3 2 1
5 4 3 2 1
 
⎕←⍋'bcdea'⋄⎕←⍋⍋'bcdea'
 
7:05 PM
@HyperNeutrino
5 1 2 3 4
2 3 4 5 1
 
⎕←⍋'eadbc' ⋄ ⎕←⍋⍋'eadbc'
 
@EriktheOutgolfer
2 4 5 3 1
5 1 4 2 3
 
so I guess it must have these two properties to be different
 
@all Can we move on to dyadic ?
 
⎕←⍋'aebdc' ⋄ ⎕←⍋⍋'aebdc'
 
7:06 PM
@EriktheOutgolfer
1 3 5 4 2
1 5 2 4 3
 
@Adám sure
 
Yes
 
⎕←⍋⍋'123456789'⋄ ⎕←⍋'123456789'
 
@RosLuP
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
 
7:09 PM
Actually, one more thing:
Since inverts itself, it is it's own inverse:
 
⍋⍋a=⍋a only if a is sorted
 
not necessarily
 
⍞←⍋6 1 4 2 5 3
 
@Adám 2 4 6 3 5 1
 
(⍋⍣¯1)6 1 4 2 5 3
 
7:10 PM
@RosLuP not always the case, sometimes that's true even when a isn't sorted
 
⍞←(⍋⍣¯1)6 1 4 2 5 3
 
@Adám 2 4 6 3 5 1
 
f⍣¯1 is inverse of f.
 
I hypothesize that ⍋⍋a=⍋a if and only if a can be sorted by only applying swaps without moving any element more than once
⎕←⍋5 1 4 2 3 ⋄ ⎕←⍋⍋5 1 4 2 3
 
@HyperNeutrino
2 4 5 3 1
5 1 4 2 3
 
7:11 PM
wait
i'm dumb
⎕←⍋4 2 3 1 6 5 ⋄ ⎕←⍋⍋4 2 3 1 6 5
 
@HyperNeutrino
4 2 3 1 6 5
4 2 3 1 6 5
 
⎕←⍋2 1 4 3 5 ⋄ ⎕←⍋⍋2 1 3 4 5
 
@EriktheOutgolfer
2 1 4 3 5
2 1 3 4 5
 
⎕←⍋2 1 4 5 3 ⋄ ⎕←⍋⍋2 1 4 5 3
 
@EriktheOutgolfer
2 1 4 3 5
2 1 4 3 5
 
7:13 PM
⎕←⍋2 1 4 5 3 ⋄ ⎕←⍋⍋2 1 4 5 3
 
@EriktheOutgolfer
2 1 5 3 4
2 1 4 5 3
 
it might seem that ⍋a=⍋⍋a iff ⍋a=a but that doesn't work when a doesn't contain all 1 to length(a)
⍋⍣¯1
 
⎕←⍋ 1 2 4 5 ⋄ ⎕←⍋⍋ 1 2 4 5
 
@RosLuP
1 2 3 4
1 2 3 4
 
Or a isn't a vector of numbers
 
7:14 PM
Anyway, let's move on.
 
true
okay :D
 
Dyadic is for character arrays only, and it grades as if the left argument was the alphabet:
⍞←{⍵['aeioubcdfghjklmnpqrstvwxyz'⍋⍵]}'helloworld'
 
@Adám eoodhlllrw
 
wait so is this essentially sort to a specific order?
 
@HyperNeutrino Yes, but a bit more fancy. I'll show.
 
7:16 PM
okay
⎕←'dbcafe'⍋'abcdef'
 
@HyperNeutrino
4 2 3 1 6 5
 
⎕←4 2 3 1 6 5⍋1 2 3 4 5 6
 
@HyperNeutrino

Rebuilding user command cache... done
Was OFF -trains=box -fns=off
⍎DOMAIN ERROR
 __field_initialize_result_←(⎕NS ⍬).⍎'⎕CY''salt''⋄⎕SE.UCMD''box on -fns=on -trains=tree''⊣enableSALT' ⋄ ⎕←4 2 3 1 6 5⍋1 2 3 4 5 6
                                                                                                        ∧

Real time: 1.096 s
User time: 1.020 s
Sys. time: 0.044 s
CPU share: 97.00 %
Exit code: 0
 
pffft
I expected that though :P
 
it only works for char arrays
 
7:17 PM
yeah
 
So how come dyadic isn't able to work on numeric arrays? Is there a specific reason?
 
If characters are missing from the alphabet, they will be considered after the alphabet, and equivalent:
⍞←'abcdefgh'⍋'hawl'
 
@Adám 2 1 3 4
 
⍞←''⍋'hello world'
 
7:19 PM
@HyperNeutrino 1 2 3 4 5 6 7 8 9 10 11
 
@Zacharý It would be possible, I guess, but not very meaningful.
Dyadic can also use multiple levels of sorting:
⎕←⍉↑'aeiou' 'bcdfghjklmnpqrstvwxyz'
 
@Adám
ab
ec
id
of
ug
 h
 j
 k
 l
 m
 n
 p
 q
 r
 s
 t
 v
 w
 x
 y
 z
 
This 2D "alphabet" means that all vowels should come before all consonants, and only if otherwise the same, the vertical order will be considered.
 
@HyperNeutrino so ''⍋⊢ is ⍳∘⍴ (at least for rank 1)
 
@Zacharý Yes, that's nice for golfing. Never thought of that. ⍬⍋ is shorter and dyadic too (good for trains).
⍞←{⍵[(⍉↑'aeiou' 'bcdfghjklmnpqrstvwxyz')⍋⍵]}'helloworld'
 
7:22 PM
@Adám eoodhlllrw
 
So this sorted all vowels before all consonants, and only then did it sort the vowels and the consonants.
 
ooh that's cool
anyway brb o/
 
⍞←{⍵[(⍉↑'aeiou' 'ebcdfghjklmnpqrstvwxyz')⍋⍵]}'helloworld'
 
@Zacharý eoodhlllrw
 
@Adám oh so won't cause a DOMAIN ERROR
 
7:24 PM
⍞←{⍵[(⍉↑'aeiou' 'bcdfghjklmnpqrstvwxyze')⍋⍵]}'helloworld'
 
@Zacharý eoodhlllrw
 
And you can have up to 15 levels of sorting using this.
 
⍞←{⍵[(⍉↑'aeiou' 'bcdfghjklmnpqrstvwxyzo')⍋⍵]}'helloworld'
 
@Zacharý eoodhlllrw
 
@Zacharý If a letter occurs more than once, then its first occurrence rules. This is useful to fill gaps in (e.g.) columns of unequal height.
@all I think that's it for . Any questions?
 
7:27 PM
Then what is the difference between {⍵[(⍉↑'aeiou' 'bcdfghjklmnpqrstvwxyz')⍋⍵]} and {⍵[('aeiou','bcdfghjklmnpqrstvwxyz')⍋⍵]}
 
what are the main uses of ⍋ in real-life/practical usage?
 
@Adám yes
 
@HyperNeutrino Sorting.
 
I don't see a reason why it should be limited to 15 levels?
it's not like each level adds one dimension to the array is it?
 
wait is there no sort monad?
 
7:28 PM
@HyperNeutrino no
 
@EriktheOutgolfer Same reason as arrays having max 15 depth rank maybe?
 
@EriktheOutgolfer Because the level increases the rank by one, and Dyalog arrays can max have rank 15.
 
@Adám oh it does?
 
@Zacharý Rank, not depth. Depth may be infinite (bound by memory only).
 
(btw Adám's pings are silent for some reason, but not others')
(and that bothers me a little bit because, well, ...)
 
7:30 PM
@EriktheOutgolfer I turned my ping sounds off. Wonder if chat is broken.
@EriktheOutgolfer How about now?
 
yes now they're audible
btw I don't think by turning your pings sounds off it should be silent for me too
 
@EriktheOutgolfer Silent?
 
@Adám yes, I think so :/ chat is notoriously buggy btw
 
@HyperNeutrino No, but I've argued that there should be one.
@EriktheOutgolfer Loud?
 
I really think there should :P
 
7:32 PM
@HyperNeutrino Why?
 
Golfing (Even though APL is not meant for golfing)
 
@HyperNeutrino btw the shortest you can get to a short monad for anything is {⍵[⍋⍵]}
 
well golfing and because having a sort builtin would be so much nicer than {⍵[⍋⍵]}
 
@Zacharý CXO says: APL is not a golfing language. Sorry!
 
so simply sorting a list is now to be considered something only useful for golfing languages?
 
7:34 PM
Yeah I know, that would be a reason it would be nice, along with ease of typing (rather than typing {⍵[⍋⍵]} every time)
 
@EriktheOutgolfer It doesn't even sort everything, only simple vectors.
 
What would be the shortest method for sorting everything then?
 
wait what does simple vector mean in this context?
 
@Zacharý J has it better: J's A⍋B is APL's B[⍋A] so you can sort B with B⍋B or ⍋⍨B.
@HyperNeutrino A non-nested list.
 
but ⍋2 3⍴3 3 6 5 3 2 works?
 
7:37 PM
@HyperNeutrino That has rank 2 but depth 1. It isn't nested, it just has two dimensions.
 
How does that work, anyways? And how many chars is J's equivalent to .
 
What if for sorting one array one has need to use a special function compare? For example, Axiom has sort(compfunction,arrayObj) if I remember well
 
⎕←⍋1 2 3 (4 5 6) 7 8 9
 
@Zacharý Two.
 
7:37 PM
@HyperNeutrino

Rebuilding user command cache... done
Was OFF -trains=box -fns=off
⍎DOMAIN ERROR
 __field_initialize_result_←(⎕NS ⍬).⍎'⎕CY''salt''⋄⎕SE.UCMD''box on -fns=on -trains=tree''⊣enableSALT' ⋄ ⎕←⍋1 2 3(4 5 6)7 8 9
                                                                                                        ∧

Real time: 1.150 s
User time: 1.070 s
Sys. time: 0.038 s
CPU share: 96.38 %
Exit code: 0
 
ah okay
 
@RosLuP I don't think there is an operator for that.
 
@HyperNeutrino That's a seven element list. It has rank 1, depth ¯2 (negative because it is unevenly nested)
 
ah ok
 
@Zacharý {⍵⌷⍨⊂⍋↑⍣≡⍵} is the shortest I've found that can sort any array that has no refs, is homogeneous, and where 15≥⍴∘⍴+|∘≡
Next one will be quick: is the same as but grades descending.
 
7:41 PM
⎕←{⍵⌷⍨⊂⍋↑⍣≡⍵}(1 2)(3 4)
 
@Zacharý
┌───┬───┐
│1 2│3 4│
└───┴───┘
 
⎕←{⍵⌷⍨⊂⍋↑⍣≡⍵}(3 4)(1 2)
 
@Adám well, I don't get that, if a builtin was added for that, why shouldn't a builtin for sorting a list shouldn't, that looks more like a golfing feature than a simple sort does...
 
@EriktheOutgolfer What? Can you fix your grammar?
 
⎕←2
 
7:42 PM
sorry
 
@Zacharý
2
 
⎕←{⍵⌷⍨⊂⍋↑⍣≡⍵}(3 4)(1 2)
 
@Zacharý
┌───┬───┐
│1 2│3 4│
└───┴───┘
 
Wait, what are refs?
 
@Adám I meant that, if there is such a built-in (⍒), then I can't get why a sort built-in doesn't exist as well, since IMO ⍒ is more of a golfing feature than a simple sort builtin
 
7:44 PM
@Zacharý Pointers to objects. That's for the OOP lesson…
 
@Adám I'll need to be there for that one.
 
@EriktheOutgolfer Do ⍒'HelloWorld' using !
 
⎕←⍋'HelloWorld' ⋄ ⎕←⍒'HelloWorld'
 
@HyperNeutrino
1 6 10 2 3 4 9 5 7 8
8 5 7 3 4 9 2 10 6 1
 
⎕←⍋⌽'HelloWorld'
 
7:46 PM
@HyperNeutrino
10 5 1 9 2 7 8 4 6 3
 
⎕←{(⌽⍒⍵)=⍋⍵}'HelloWorld'
 
@Zacharý
1 1 1 1 0 1 0 0 0 1
 
⎕←{(⍒⌽⍵)=⍋⍵}'helloworld'
 
@Zacharý
0 0 0 0 0 0 0 0 0 0
 
⎕←{(⌽⍒⍵)=⍋⍵}'helloworld'
 
7:48 PM
@Zacharý
1 1 1 0 1 0 0 0 1 1
 
@Zacharý OK, can we move on?
 
Yes
 
Reverse compose ⍒=⍋
 
That was what I just was going testing, RosLuP
 
7:50 PM
OK, let's see if we can cover .
Monadic is the index generator. ⍳a generates an array of shape a where the elements are the indices for that element:
⍞←⍳10
 
@Adám 1 2 3 4 5 6 7 8 9 10
 
⎕←⍳2 4
 
@Adám
┌───┬───┬───┬───┐
│1 1│1 2│1 3│1 4│
├───┼───┼───┼───┤
│2 1│2 2│2 3│2 4│
└───┴───┴───┴───┘
 
⎕←⍳2 3 4
 
@HyperNeutrino
┌─────┬─────┬─────┬─────┐
│1 1 1│1 1 2│1 1 3│1 1 4│
├─────┼─────┼─────┼─────┤
│1 2 1│1 2 2│1 2 3│1 2 4│
├─────┼─────┼─────┼─────┤
│1 3 1│1 3 2│1 3 3│1 3 4│
└─────┴─────┴─────┴─────┘
┌─────┬─────┬─────┬─────┐
│2 1 1│2 1 2│2 1 3│2 1 4│
├─────┼─────┼─────┼─────┤
│2 2 1│2 2 2│2 2 3│2 2 4│
├─────┼─────┼─────┼─────┤
│2 3 1│2 3 2│2 3 3│2 3 4│
└─────┴─────┴─────┴─────┘
 
7:52 PM
⎕←⍴⍳2 3 4
 
@Zacharý
2 3 4
 
yeah monadic ⍴∘⍳ is the same as monadic
 
Any bets on what ⍳0 gives?
 
⍬ ?
 
7:54 PM
i'm guessing that's empty list?
 
@Zacharý Yes. And what about ⍳0 0?
@HyperNeutrino Yes.
 
ok
@Adám ⍬ as well?
 
⎕←⍳0 0
 
@Adám 0 0⍴⍬?
 
@EriktheOutgolfer

Rebuilding user command cache... done
Was OFF -trains=box -fns=off

Real time: 1.051 s
User time: 0.983 s
Sys. time: 0.036 s
CPU share: 97.05 %
Exit code: 0
 
7:55 PM
@HyperNeutrino Nope. remember that the result must have the same shape as the argument.
@dzaima Yes.
 
@EriktheOutgolfer What explains that then?
 
@Adám doesn't seem like it
      0 0⍴⍬
┌⊖┐
⌽0│
└~┘
      ⍳0 0
┌⊖──────┐
⌽ ┌→──┐ │
│ │0 0│ │
│ └~──┘ │
└∊──────┘
 
@EriktheOutgolfer The reason for this strange result is that there is nothing to show, so the bot gives you the debug info instead.
 
@Adám that's why RIDE is useful to have
 
7:56 PM
⎕←⍳0 0⊣⎕SE.UCMD'box on -s=max'
 
@Adám
┌⊖──────┐
⌽ ┌→──┐ │
│ │0 0│ │
│ └~──┘ │
└∊──────┘
 
@EriktheOutgolfer Uh, you shouldn't be programming using a chat bot. Yes, use the desktop version and either the terminal interface, RIDE or (on Windows) the IDE.
 
@Adám I'll install IDE too, when I sometime boot into Windows :-P
 
@dzaima Oh, no it isn't 0 0⍴⍬ because each element must have two element (coordinates), and in 0 0⍴⍬ each element has only one.
 
it's not a priority for me to request a new license for Windows currently
 
7:59 PM
0 0⍴(⍬ ⍬)?
 
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