feat: add `blas/ext/join-between` by headlessNode · Pull Request #11287 · stdlib-js/stdlib

headlessNode · 2026-04-03T20:25:44Z

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Resolves stdlib-js/metr-issue-tracker#238.

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add blas/ext/join-between

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Resolves [RFC]: add blas/ext/join-between metr-issue-tracker#238

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Primarily written by Claude Code but with heavy back-and-forth fixing.

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stdlib-bot · 2026-04-03T20:28:58Z

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kgryte · 2026-04-04T07:12:07Z

lib/node_modules/@stdlib/blas/ext/join-between/lib/main.js

+* @param {string} [options.prefix=''] - prefix to prepend to each joined string
+* @param {string} [options.suffix=''] - suffix to append to each joined string


These should both be allowed to be ndarrays. What if I want to prefix each joined string with different prefixes? Ditto for suffix.

kgryte · 2026-04-04T07:16:42Z

lib/node_modules/@stdlib/blas/ext/join-between/lib/main.js

+	if ( opts.separators.length === 1 ) {
+		separators = broadcastScalar( opts.separators[ 0 ], 'generic', [ 1 ], order );
+	} else {
+		separators = new ndarray( 'generic', opts.separators, [ opts.separators.length ], [ 1 ], 0, order );
+	}


What's going on here? Why isn't separators being broadcast against the entire input array x? What if I want different separators for each row in a matrix?

The broadcasting logic may be a bit nuanced here. Namely because the separators array needs to broadcast to a shape which accounts for the number of separators needing to be one less than the number of elements to be joined.

...this will mean computing the number of elements along the reduced dimensions of the input ndarray and then broadcasting the separators array against [ ..., M-1 ], where ... corresponds to the non-reduced dimensions and M corresponds to the number of elements along the reduced dimensions.

kgryte · 2026-04-04T07:17:38Z

lib/node_modules/@stdlib/blas/ext/join-between/lib/main.js

+		separators = new ndarray( 'generic', opts.separators, [ opts.separators.length ], [ 1 ], 0, order );
+	}
+	// Perform the reduction:
+	unaryReduceStrided1d( dispatch, [ x, y ], opts.dims );


This is odd. Why are you doing it this way? A closure should not be necessary if you have done broadcasting correctly.

Using unaryReduceStrided1d and not *-dispatch and not -factory skips a bunch of validation logic that would have to be reimplemented here. That is not desirable. Ideally, we'd figure out a way to use the *-factory package.

Validation including acceptable dtypes. TL;DR: there is a lot currently incorrect with this implementation.

kgryte · 2026-04-04T07:18:16Z

lib/node_modules/@stdlib/blas/ext/join-between/lib/main.js

+	* @param {Array<Object>} arrays - ndarrays
+	* @returns {string} joined string
+	*/
+	function dispatch( arrays ) {


This function should not be necessary. prefix, suffix, and separators should all be passed down as auxiliary arrays via unaryReduceStrided1d, not via a closure like this.

Hmm...but I see that separators will be problematic here, as unaryReduceStrided1d assumes all ancillary arrays are 0D, while separators will always be 1D.

It's possible that we need only tweak unary-reduce-strided1d slightly here.

@kgryte I think two changes in unary-reduce-strided1d would unlock the factory approach:

Allow arrays with extra trailing dimensions here: https://github.com/stdlib-js/stdlib/blob/develop/lib/node_modules/%40stdlib/ndarray/base/unary-reduce-strided1d/lib/main.js#L380

Pass K here: https://github.com/stdlib-js/stdlib/blob/develop/lib/node_modules/%40stdlib/ndarray/base/unary-reduce-strided1d/lib/main.js#L428, and for array with more than K dimensions, preserved trailing dimensions instead of collapsing to 0d.

I believe the iteration code would work as is. Should I go ahead with these changes in unary-reduce-strided1d? and the binary-* counterpart as well?

Those changes are not sufficient. It is not just main.js which needs to be updated. I'll try and take a look.

@headlessNode The following commit c8df03c should now allow passing the separators ndarray as a 1D array to the lower-level strided reduction interface.

kgryte

Left initial comments.

kgryte · 2026-04-08T02:42:25Z

/stdlib merge

kgryte · 2026-04-08T02:56:35Z

lib/node_modules/@stdlib/blas/ext/join-between/lib/main.js

+* @param {Options} [options] - function options
+* @param {string} [options.prefix=''] - prefix to prepend to each joined string
+* @param {string} [options.suffix=''] - suffix to append to each joined string
+* @param {ArrayLikeObject} [options.separators=[',']] - separators


Separators should be an ndarray. But also, why is separators optional here? Shouldn't it be mandatory? If users just want to join elements with a single separator, they can use blas/ext/join. I think it is fine to leave prefix and suffix as optional, but we should make provided separators be a mandatory positional argument.

headlessNode added Feature Issue or pull request for adding a new feature. METR Pull request associated with the METR project. labels Apr 3, 2026

stdlib-bot added BLAS Issue or pull request related to Basic Linear Algebra Subprograms (BLAS). Needs Review A pull request which needs code review. labels Apr 3, 2026

headlessNode requested a review from kgryte April 3, 2026 20:29

github-actions bot mentioned this pull request Apr 4, 2026

[aw] No-Op Runs #11033

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kgryte added Needs Changes Pull request which needs changes before being merged. and removed Needs Review A pull request which needs code review. labels Apr 4, 2026

stdlib-bot added the bot: In Progress Pull request is currently awaiting automation. label Apr 8, 2026

Merge remote-tracking branch 'upstream/develop' into blas/nd-joinbetween

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stdlib-bot removed the bot: In Progress Pull request is currently awaiting automation. label Apr 8, 2026

kgryte reviewed Apr 8, 2026

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		* @param {string} [options.prefix=''] - prefix to prepend to each joined string
		* @param {string} [options.suffix=''] - suffix to append to each joined string

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