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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 isnan = require( '@stdlib/math/base/assert/is-nan' );
// MAIN //
/**
* Calculates the arithmetic mean of a double-precision floating-point strided array according to a mask.
*
* @param {PositiveInteger} N - number of indexed elements
* @param {Float64Array} x - input array
* @param {integer} strideX - `x` stride length
* @param {NonNegativeInteger} offsetX - `x` starting index
* @param {Uint8Array} mask - mask array
* @param {integer} strideMask - `mask` stride length
* @param {NonNegativeInteger} offsetMask - `mask` starting index
* @returns {number} arithmetic mean
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
* var Uint8Array = require( '@stdlib/array/uint8' );
*
* var x = new Float64Array( [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
* var mask = new Uint8Array( [ 0, 0, 0, 0, 0, 0, 0, 0, 1, 1 ] );
*
* var v = dmskmean( 5, x, 2, 1, mask, 2, 1 );
* // returns 1.25
*/
function dmskmean( N, x, strideX, offsetX, mask, strideMask, offsetMask ) {
var sum;
var ix;
var im;
var mu;
var v;
var i;
var n;
var c;
if ( N <= 0 ) {
return NaN;
}
n = 0;
sum = 0.0;
ix = offsetX;
im = offsetMask;
for ( i = 0; i < N; i++ ) {
if ( mask[ im ] === 0 ) {
v = x[ ix ];
if ( isnan( v ) ) {
return v;
}
sum += v;
n += 1;
}
ix += strideX;
im += strideMask;
}
if ( n === 0 ) {
return NaN;
}
mu = sum / n;
c = 0.0;
ix = offsetX;
im = offsetMask;
for ( i = 0; i < N; i++ ) {
if ( mask[ im ] === 0 ) {
c += x[ ix ] - mu;
}
ix += strideX;
im += strideMask;
}
return mu + ( c / n );
}
// EXPORTS //
module.exports = dmskmean;
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