[RFC]: add @stdlib/array/base/cusome-by-right

[kgryte]

Description

This RFC proposes adding the package @stdlib/array/base/cusome-by-right, which cumulatively tests whether at least n array elements in a provided array pass a test implemented by a predicate function, while iterating from right-to-left. The function should return a new generic array. The package should also provide an #assign API for setting output values in a provided output array.

function isPositive( value ) {
	return ( value > 0 );
}

var x = [ 1, 1, 0, 0, 0 ];

var y1 = cusomeByRight( x, 2, isPositive );
// returns [ false, false, false, false, true ]

var y2 = [ false, null, false, null, false, null, false, null, false, null ];
var out = cusomeByRight.assign( x, 2, y2, 2, 0, isPositive );
// returns [ false, null, false, null, false, null, false, null, true, null ]

var bool = ( out === y2 );
// returns true

where the assign API supports an offset and stride (see, e.g., @stdlib/array/base/take). Note that, by iterating from right to left, the values in the output array are equivalent to having first reversed the input array x and then using left-to-right iteration.

Both APIs should support accessor arrays (see, e.g., @stdlib/array/base/take).

Related Issues

No.

Questions

No.

Other

• See also @stdlib/utils/some-by-right

Checklist

• I have read and understood the Code of Conduct.
• Searched for existing issues and pull requests.
• The issue name begins with RFC:.

[stdlib-bot]

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[GittyHarsha]

Hi,
is it expected to use @stdlib/utils/some-by-right to implement @stdlib/array/base/cusome-by-right ?
If so, doesn’t this approach result in quadratic time complexity?

[kgryte]

@GittyHarsha No, you should not use @stdlib/utils/some-by-right to implement the proposed API. The implementation should be similar to other similar packages in @stdlib/array/base.

[GittyHarsha]

Hi,
I got a doubt while implementing the #assign API.
In reference to @stdlib/array/base/take/lib/assign.js,
the accessor arrays of type complex and boolean are explicitly handled.
I think for @stdlib/array/base/cusome-by-right, there is no need to explicitly handle any types of accessor arrays?

[kgryte]

@GittyHarsha You do need to handle accessor arrays; however, I think you are right that you don't need to special case either ComplexXXArrays or BooleanArray.

E.g., in https://github.com/stdlib-js/stdlib/blob/develop/lib/node_modules/%40stdlib/array/base/cuany/lib/assign.js, we special case complex and boolean arrays, with a fallback to a general accessor utility. For your case, I think you only need the general accessor utility.