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Comment by mlochbaum | Hacker News Reader

> Its powerful array manipulation primitives can easily be brought forward into a language with modern syntax, and haven't they?

Kind of. The languages that one might expect to do this (Julia, R, NumPy) have picked out a few things from APL in an inconsistent way, leaving a lot as well. For example most are missing the generalization of prefix sum that APL calls "scan". So in [0], Conor was able to translate some code to every language in the APL family but not yet any outside of it. Another one, I don't think I've ever seen Replicate[1] outside the APL family. It's a generalization of filter to take an arbitrary count instead of 0 or 1 that's often useful if you know about it.

[0] https://github.com/codereport/array-language-comparisons/blo...

[1] https://mlochbaum.github.io/BQN/doc/replicate.html

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Julia spells "scan" as "accumulate". I don't think we have something exactly like replicate out of the box, but it's a one-line function definition away:

     replicate(inds, v) = mapreduce(((i, n),) -> fill(v[i], n), vcat, enumerate(inds))

I agree with the spirit of your point though. Having operations like this as part of your 'alphabet' can be a really powerful thing. That's why I think APL is really well suited to being a domain specific language embedded in a language like julia. Shashi took a stab at this a few years ago, but it'd be nice to revive it: https://github.com/shashi/APL.jl

R has `rep` for replicate:

    rep(c("a", "b", "c", "d"), c(2, 1, 0, 2))
    c("a", "a", "b", "d", "d")

Replicate looks like numpy's repeat. For example

  np.repeat(list("abcd"), [2,1,0,2])

is equivalent to the first example in the link.

Ah, thank you! I'd tried to find this for implementing BQN in NumPy (never finished) and didn't. Maybe I thought it only worked with a scalar for the number of repetitions.

I can't make head or tails of the first links, so I'll leave experts to it. The second one, yeah, it's nice syntaxical sugar, but it can be replicated very easily (map + "constant list" + concatenate). And versions of it exist in many languages - even C# has SelectMany https://learn.microsoft.com/en-us/dotnet/api/system.linq.enu...

All the good APL functions can be implemented easily (but please, they're just built-in functions, not syntactic sugar!). It's the selection of which functions to implement that makes it so much better for working with arrays.

"even C#" seems to imply you have less obscure examples than a function in a Linq package, is this the case? I admit I've never looked into Linq but I do see it come up in array language discussions sometimes. It's possible it has a more APL-like philosophy for a slightly different use case. The other difference is that APL uses a function on two arrays, which is nice because you can easily filter based on, say, the previous element.

EDIT: No, the C# function seems to only do the mapping and concatenation and doesn't even take a number of copies, that's really not the same.

Numpy has replicate (numpy.repeat).

Excel has SCAN.

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