The APL Orchard

11:24 AM

@B.Wilson what is this used for?

2 hours later…

RubenVerg

1:34 PM

any decent way to tacitly write (XfY)g(YfX)?

I guess there's nothing better than a fork but I don't want to repeat the expression for f

LdBeth

2:19 PM

usually, the specific content f and g is required to derive a better expression

if f isn't commutative, is X f Y the complement of Y f X?

but the easy way is just do f←

finooiigee

2:49 PM

@RubenVerg No, other than f g f⍨

3:00 PM

Welcome to APL Quest 2019-2!* Today's quest is Making the Grade:

> Write a function that, given an array of integer test scores in the inclusive range 0–100, returns an identically-shaped array of the corresponding letter grades according to the table to the left.
Score Letter
Range Grade
0–64 F
65–69 D
70–79 C
80–89 B
90–100 A

Just the standard solution...
{'FDCBA'⌷⍨⊂1+65 70 80 90⍸ ⍵}

Yeah can't go wrong with that

What's the arbitrary decision you have to make when making this solution?

Hint: it could save you a 1+

⎕IO←1

wasn't thinking of ⎕IO

more arbitrary than that

you could use 0 65 70 80 90 as intervals?

3:06 PM

Yeah exactly

And what if you didn't have interval index ⍺⍸⍵?

'FDCBA'⌷⍨∘⊂+/⍤≥⍤0 1∘0 65 70 80 90

∧\⍵∘.≥

ah, didn't think of outer product

Yeah that's basically what interval index is as a pattern

+⌿∘.≤

@RikedyP better :)

3:11 PM

@rabbitgrowth This is outer product for these ranks spelled out using rank, to be fair

Any weird ones? I didn't think of any

no, not me. You already forced me to think of another one ;)

We run a tight ship around here, gotta crack the whip occasionally

As it shoudl be!

This one's used an example to contrast with control structures in course.dyalog.com/user-defined-functions/#marking-tests, but obviously there's not much to be gained in APL by doing so

 grades←Grade2 scores;boundaries;score
 boundaries←0 65 70 80 90
 grades←⍬
 :For score :In scores
     :If 90≤score
         grades,←'A'
     :ElseIf 80≤score
         grades,←'B'
     :ElseIf 70≤score
         grades,←'C'
     :ElseIf 65≤score
         grades,←'D'
     :ElseIf 0≤score
         grades,←'F'
     :EndIf
 :EndFor

After more than one year resetting my brain not using for-loops and if-then-esle you present this?

3:20 PM

hahaha

]runtime -c "Grade 0 64 65 69 70 79 80 89 90 100" "Grade2 0 64 65 69 70 79 80 89 90 100"

Grade 0 64 65 69 70 79 80 89 90 100 → 9.8E¯7 | 0% ⎕⎕⎕
Grade2 0 64 65 69 70 79 80 89 90 100 → 1.2E¯5 | +1071% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕

Well anyway, unless anyone else has any urgent pressing matters, I might call it for this one

See you next week for the similarly themed 2019-3 Grade Distribution problems.tryapl.org/psets/2019.html?goto=P3_Grade_Distribution

Can I ask antoher not related question? I do not fully understand (the use) of the left argument of ⌸. Can be abnother time also, np

it's different in monadic and dyadic case

yes exactly. But do not see the added value of the dyadic version

I do need to go soon but can do this one quick

It's so you can group by keys which aren't the data

But then why should the size of left and roght argument be the same

3:25 PM

it's one major cell key in ⍺ for each corresponding major cell in ⍵

apples ← 2 0 1 5 3

groups ← 'AACBC'

total apples in each group

ah, ok!

hope that makes sense

yes ,thanks

catch you later, then!

@RikedyP {('FDCBA'/⍨¯2-/0 65 70 80 90 101)[1+⍵]}

3:32 PM

@rabbitgrowth :) !!