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* @license Apache-2.0
*
* Copyright (c) 2020 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 covariance = require( '@stdlib/stats/incr/covariance' );
var isnan = require( '@stdlib/math/base/assert/is-nan' );
// MAIN //
/**
* Returns an accumulator function which incrementally computes a sample covariance.
*
* @returns {Function} accumulator function
*
* @example
* var nancovariance = require( '@stdlib/stats/incr/nancovariance' );
*
* var acc = nancovariance();
*
* var cov = acc();
* // returns null
*
* cov = acc( 2.0, 1.0 );
* // returns null
*
* cov = acc( NaN, 5.0 );
* // returns null
*
* cov = acc( 4.0, 5.0 );
* // returns 4.0
*
* cov = acc();
* // returns 4.0
*/
function nancovariance() {
var count = 0;
var acc = covariance();
return accumulator;
/**
* Updates and returns the sample covariance when provided two numeric arguments.
* If no arguments are provided, returns the current sample covariance.
*
* @private
* @param {number} [x] - new x value
* @param {number} [y] - new y value
* @returns {(number|null)} sample covariance or null
*/
function accumulator( x, y ) {
var val;
if ( arguments.length === 0 ) {
return ( count < 2 ) ? null : acc();
}
if ( isnan( x ) || isnan( y ) ) {
return ( count < 2 ) ? null : acc();
}
count += 1;
val = acc( x, y );
return ( count < 2 ) ? null : val;
}
}
// EXPORTS //
module.exports = nancovariance;
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