Chris Pearson chrispsn

Transitive Closure in k

In The APL Orchard, ngn said:

the or-dot-and [∨.∧] trick is one of the most beautiful apl expressions ever, worth staring at :)

Well I had better learn it then...

Apparently it computes a transitive closure of a binary relation. Let's hit Wikipedia.

Analytics on k code

Mildly interesting results from string analysis of a handful of k files. If you have more public k files or suggestions for further analysis, comment below!

This uses the latest Shakti.

Corpus:

kparc's Advent of Code answers from 2015
ngn's Advent of Code answers from 2015 and 2019
ngn's Project Euler answers

k9 dicts (WIP)

Current in k9 2020.03.27.

Standard lookup:

 [a:1;b:2]`b
2

k tech tree

Thought experiment:

Which k primitives can be implemented as k-strings, reasonably efficiently, with a handful of 'native' built-ins?

Not verified to be in dependency order yet... may depend on the choice of 'fundamental' primitives. Need to do speed tests too.

k9 syntax (download via Shakti). Got a better way to write one? Feel free to comment, you'll be credited!

Excel Tables and VBA

It's 2020, and there's now many ways to work with data of arbitrary length in Excel:

Power Query's M language
JavaScript
dynamic arrays.

But if you use or support older Excel versions, VBA can still be useful.

WAR ON RAZE

This is the story of what happened when I went down a rabbit hole.

It starts with k7. If you press Ctrl-] in the k7 WASM console, this appears:

x^x*/:x:2_!100

That's a prime number filter. There are faster ones - kparc.com's x,1_&&/80#'!:'x is beautiful - but this one is really short.

We need to talk about group.

I'm sorry to tell you, but group is gone.

If you check out the latest k.d on shakti.com as at 28 March 2023, you'll see that 'unary' = is now 'freq' (frequency).

Group had a long life: it's been around since at least k2, or 1996.

So why did group go? And what should we use instead?

K: Default dicts?

Code examples are in ngn/k, a dialect where int null is 0N and a list find miss is 0N, not #list.

It would be nice if a grouped list gave empty int list for an outdex, and outdex of frequency gave zero. (See here for more.)

 x:="abracadabra"

	# Unevaluated

	A `wrap attribute that causes overindexing to auto-mod based on length of list.
	Avoids mismatch of behaviour of i# and -i#. Cut will auto-fill if not long enough.
	Negative indexing wraps backwards: (`wrap"abc")[-1] is "c"
	Requires `null to go back to default behaviour?

	## Slice as basis for lots of primitives

	Inspired by ngn's https://chat.stackexchange.com/transcript/message/59004538#59004538 ...