feat: add ndarray/splice

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Resolves stdlib-js/metr-issue-tracker#135.

Description

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This pull request:

• add ndarray/splice

Related Issues

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This pull request has the following related issues:

• Resolves [RFC]: add ndarray/splice metr-issue-tracker#135
• Progresses [RFC]: achieve ndarray API parity with built-in JavaScript arrays  #2656

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Coverage Report

Package	Statements	Branches	Functions	Lines
ndarray/splice	$\color{red}442/461$ $\color{green}+0.00\%$	$\color{red}73/79$ $\color{green}+0.00\%$	$\color{green}4/4$ $\color{green}+0.00\%$	$\color{red}442/461$ $\color{green}+0.00\%$

The above coverage report was generated for the changes in this PR.

[kgryte]

This is doing a lot more work than it needs to. You are effectively creating multiple slice objects per iteration only to retrieve the single slice you are interested in. This seems wasteful, as the dimensions other than dim are ignored and useless.

The following logic is effectively what you are interested in:

stdlib/lib/node_modules/@stdlib/slice/base/normalize-multi-slice/lib/main.js

Line 40 in 8879b1d

function normalize( value, len, strict ) {

You have four choices.

1. You can either reimplement that logic here. This is straightforward.
2. You can create a multislice having a single dimension. Although, then you effectively pay the penalty of calling args2multislice twice (once to create a multislice to be normalized and twice to create the normalized multislice) for each iteration of the loop.
3. You can create a separate utility for this sort of use case. E.g., something like normalize-multi-slice-arguments where we pull out the logic from above and then make normalize-multi-slice a thin wrapper around that utility. Then you'd do something like normalizeMultiSliceArguments( [ sliceList[ i ] ], [ sh[ dim ] ], true ).
4. But perhaps the most straightforward of all which avoids a loop here altogether is to realize that args2multslice doesn't care whether the arguments actually correspond to the ndarray. So you can do something like

// Create a "shape" for the express purpose of validating each of the slice arguments:
sh = filled( shape[ dim ], sliceList.length );

// Create an un-normalized multislice:
ms = args2multislice( sliceList );

// Normalize the multislice:
S = normalizeMultiSlice( ms, sh, true );

if ( S.code ) {...}

return S.data;