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Comment by bear8642 | Hacker News Reader

> "learn an array language, they're easy to write on paper" everyone would think they were insane... but there is something to it, in certain cases.

Indeed, and sometimes not needing a computer to quickly splash out an idea you're thinking/talking about is extremely useful!

Over Christmas, I showed my brother {+⌿⍤2(∘.≤)⍤1⍨⍵} as a small expression to explore attribute to pick playing Top-Trumps admist a discussion. Not something you'd be able to do in many other languages!

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Could you explain the expression to us?

Sure - idea is you've got a 6×30 matrix of the 6 card attributes for each of the 30 cards, and want to know for each attribute how many other cards they'd beat.

  {+⌿⍤2(∘.≤)⍤1⍨⍵}

  {            ⍵} ⍝ single argument (monadic) function with argument ⍵
  {           ⍨⍵} ⍝ "selfie" - ⍵ f ⍵ where f is (∘.≤)⍤1
  {         ⍤1⍨⍵} ⍝ on each row (1 dimensional element)
  {    (∘. )⍤1⍨⍵} ⍝ cartesian (outer) product of each row with itself
  {    (∘.≤)⍤1⍨⍵} ⍝ ≤ comparison of those elements - produces 6 30×30 boolean matrices
  {  ⍤2(∘.≤)⍤1⍨⍵} ⍝ on each of those matricies (2 dimensional element)
  {+⌿⍤2(∘.≤)⍤1⍨⍵} ⍝ sum the columns

leading to: {+⌿⍤2(∘.≤)⍤1⍨⍵} ⍝ compare each row (⍤1) to itself (⍨) and count (+⌿) how many cards that beats

That make sense?

That's great and you have sent me down the rabbit hole.

So, usage would be something like:

CardPower ← {+⌿⍤2(∘.≤)⍤1⍨⍵}

CardPower cardMatrix

Yep, or even apply inline as {+⌿⍤2(∘.≤)⍤1⍨⍵}cardMatrix

Thinking about your comment further (and having read TFA and some of the comments) inline usage does seem to make more sense as it's only a few more characters. In that way it's transparent. Decreasing indirection (assuming that the operators always function simply and plainly.

Thanks for that follow up comment.

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