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Adám
Adám
1:00 PM
Welcome to APL Quest 2017-8! Today's quest is Be the First 1:
> Write a dfn that takes a Boolean vector or scalar and “turns off” all the 1s after the first 1.
This should be quick.
 
Richard
Richard
<\
:)
 
Adám
Adám
That's all folks!
What if you couldn't use that?
 
Richard
Richard
tried as alternative using ⊃⍸ for finding fist postition of the 1
 
Adám
Adám
Ah yes, good approach.
 
Richard
Richard
and than inserting it into vector of same length filled woth 0's
 
Adám
Adám
1:02 PM
We had an intern add old problem sets to the automated site. He was quite new to APL, so you've got to give him A for effort on {⍵{(↑⍵↑⍺),((≢⍺)-⍵)⍴0}+/⍸(⍋⍋⍵)=1+(≢⍵)-+/⍵}
 
Richard
Richard
wow
 
Adám
Adám
@Richard Will have issues with arguments that have no 1.
 
Richard
Richard
yes true
 
Adám
Adám
Huh, there's a missing test case.
 
Richard
Richard
single 1?
 
dzaima
dzaima
1:05 PM
@Adám ((⊢>¯1↓0,⊢)∨\)
 
Adám
Adám
@Richard Yes.
@dzaima That's very good, but using a different Boolean scan…
 
dzaima
dzaima
@dzaima (translating from BQN ≠⟜»∨`)
@Adám but it's one that doesn't use the left-to-right-to-left-ness of APLs scan
 
Adám
Adám
True.
 
dzaima
dzaima
⍳∘≢=⍳∘1
 
Adám
Adám
Fails on scalars, but otherwise good.
Industrial strength solution: ⍎'1(.*)'⎕R{'1 ',2↓'0 '⍴⍨⊃⍵.Lengths}⍤⍕,',⍬'⍨
@Richard Huh, the reference solution is even wrong!
 
Richard
Richard
1:13 PM
⊃⊖{⍵}⌸
instead of ⊃⍸
for the first 1
 
Adám
Adám
Fun. {⍵} is ⊢ btw.
@Richard Fails on 1 0
 
Richard
Richard
I stilll don't fully understand {⍺⍵} just left from an operator. I can use it but don't understand the logic.
 
Adám
Adám
@dzaima Fixed: {r⊣(,r)←(⍳≢⍵)=1⍳⍨,r←⍵}
@Richard {⍺⍵} is no different from any other function. It is the same as ,⍥⊂
 
Richard
Richard
The ⍺ and ⍵ magically are retreived from the operator on the right?
 
Adám
Adám
Not sure what you're asking.
 
Richard
Richard
1:18 PM
Where do the ⍺ ⍵ get their values from? 
{⍺⍵}⌸
 
dzaima
dzaima
@Adám ⍴⍴⍳∘≢=1⍳⍨, if you really want to support the useless case
 
Adám
Adám
D'oh. Yes.
@Richard Every operator is different. Monadic f⌸ applies f once for each unique major cell in the argument. The left argument given to f is the unique major cell, and the right argument is the list of indices where that cell occurs in the argument.
 
dzaima
dzaima
@Richard where does {⍺⍵}¨ get ⍺ & ⍵ from? where does ∘.{⍺⍵} get their ⍺ & ⍵ from? answer: operators can just decide to give whatever arguments they want to their operands
 
Richard
Richard
I should see {⍺⍵} as a function of course which is input for the operand
 
Adám
Adám
Indeed. Although we tend to say "operands" for operator inputs.
 
Richard
Richard
1:25 PM
and that explains using ⊢ intead of {⍵}, both are functions or operands for the operator
 
Adám
Adám
Exactly.
 
Richard
Richard
and the right operand of ⌸ is not a function but a matrix.
 
Adám
Adám
⌸ is a monadic operator, it has no right operand.
@147pm Welcome to the APL Orchard. Did you solve your keyboard problem?
 
Richard
Richard
oh yes, so the operator with its left operand results in a new derived functon which takes an aray as its right argument
 
Adám
Adám
That's correct.
And on that note, I think we can end this week's episode. See you next week for 2017-9: Double Trouble.
 
Richard
Richard
1:30 PM
thanks, till next week
 
 
6 hours later…
Stack Exchange Feeds
Stack Exchange Feeds
7:24 PM
0
Q: I need to most efficiently insert a number in a maintained large sorted variable. Is there a better method than test1?

creaturaltest1 is quite a bit faster vs test2 which is just to append a variable then resort. q←⍳1000000 ⋄ q←10 9 8 7 6 5 4 3 2,q ⍝q is kept sorted test1←{ y←⍺(⍳∘1≤)⍵ ⍝ very fast (y↑⍺),⍵,(y↓⍺) ⍝ is there a tacit version here and without copying? } 10↑q test1 6 10 9 8 7 6 6 5 4 3 2 cmpx 'q test1 6' 3.2E...

apl
 
 
2 hours later…
AviFS
AviFS
9:15 PM
In SETL, the conventional program for the factorial of n is */[1..n], according to the Wikipedia page. But APL isn't listed as an influence, nor any APL derivative. It's not mentioned anywhere on the page, actually. Should it be?
SETL
SETL (SET Language) is a very high-level programming language based on the mathematical theory of sets. It was originally developed by (Jack) Jacob T. Schwartz at the New York University (NYU) Courant Institute of Mathematical Sciences in the late 1960s. == Design == SETL provides two basic aggregate data types: unordered sets, and sequences (the latter also called tuples). The elements of sets and tuples can be of any arbitrary type, including sets and tuples themselves. Maps are provided as sets of pairs (i.e., tuples of length 2) and can have arbitrary domain and range types. Primitiv...
 

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