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* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var isPositiveZero = require( '@stdlib/math/base/assert/is-positive-zero' );
var gcopy = require( '@stdlib/blas/base/gcopy' ).ndarray;
var gminheapify = require( '@stdlib/blas/ext/base/gminheapify' ).ndarray;
var gminheapSiftDown = require( '@stdlib/blas/ext/base/gminheap-sift-down' ).ndarray;
// MAIN //
/**
* Computes the `k` maximum values of a strided array.
*
* ## Notes
*
* - If `N <= 0`, the function fills the output array with `NaN`.
* - If `k <= 0`, the function returns the output array unchanged.
* - The function distinguishes between positive zero (`+0`) and negative zero (`-0`), treating positive zero as greater than negative zero when values are otherwise equal.
* - The min-heap algorithm is sensitive to the presence of `NaN` values. Since `NaN` comparisons always return `false`, if `NaN` values are present in the input array, the results will be unpredictable.
*
* @private
* @param {PositiveInteger} N - number of indexed elements
* @param {PositiveInteger} k - number of maximum values to return
* @param {Object} x - input array object
* @param {Collection} x.data - input array data
* @param {Array<Function>} x.accessors - array element accessors
* @param {integer} strideX - stride length for `x`
* @param {NonNegativeInteger} offsetX - starting index for `x`
* @param {Object} out - output array object
* @param {Collection} out.data - output array data
* @param {Array<Function>} out.accessors - array element accessors
* @param {integer} strideOut - stride length for `out`
* @param {NonNegativeInteger} offsetOut - starting index for `out`
* @returns {Object} output array object
*
* @example
* var toAccessorArray = require( '@stdlib/array/base/to-accessor-array' );
* var arraylike2object = require( '@stdlib/array/base/arraylike2object' );
*
* var x = [ 1.0, 2.0, 3.0, 4.0, 5.0 ];
* var out = [ 0.0, 0.0, 0.0 ];
*
* maxk( x.length, 3, arraylike2object( toAccessorArray( x ) ), 1, 0, arraylike2object( toAccessorArray( out ) ), 1, 0 );
* // out => [ 3.0, 4.0, 5.0 ]
*/
function maxk( N, k, x, strideX, offsetX, out, strideOut, offsetOut ) {
var xbuf;
var obuf;
var xget;
var oget;
var oset;
var min;
var ix;
var i;
var v;
xbuf = x.data;
obuf = out.data;
xget = x.accessors[ 0 ];
oget = out.accessors[ 0 ];
oset = out.accessors[ 1 ];
// Copy first k elements from input to output:
gcopy( k, xbuf, strideX, offsetX, obuf, strideOut, offsetOut );
// Build min-heap from first k elements in output...
gminheapify( k, obuf, strideOut, offsetOut );
// Cache minimum value:
min = oget( obuf, offsetOut );
// Scan remaining elements and update heap if larger than current minimum...
ix = offsetX + ( k * strideX );
for ( i = k; i < N; i++ ) {
v = xget( xbuf, ix );
// If element is larger than min, replace root and sift down...
if ( v > min || (v === min && isPositiveZero( v )) ) {
oset( obuf, offsetOut, v );
gminheapSiftDown( k, 0, v, obuf, strideOut, offsetOut );
min = oget( obuf, offsetOut );
}
ix += strideX;
}
return out;
}
// EXPORTS //
module.exports = maxk;
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