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* @license Apache-2.0
*
* Copyright (c) 2018 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' );
var increwvariance = require( '@stdlib/stats/incr/ewvariance' );
// MAIN //
/**
* Returns an accumulator function which incrementally computes an arithmetic mean, ignoring `NaN` values.
*
* @param {number} alpha - smoothing factor
* @returns {Function} accumulator function
*
* @example
* var incrnanewvariance = require( '@stdlib/stats/incr/nanewvariance' );
*
* var accumulator = incrnanewvariance( 0.5 );
*
* var v = accumulator();
* // returns null
*
* v = accumulator( 2.0 );
* // returns 0
*
* v = accumulator( 4.0 );
* // returns 1.0
*
* v = accumulator( NaN );
* // returns 1.0
*
* v = accumulator( 5.0 );
* // returns 1.5
*
* v = accumulator();
* // returns 1.5
*/
function nanewvariance(alpha) {
var acc = increwvariance( alpha );
return accumulator;
/**
* Updates and returns the exponentially weighted variance when provided a numeric input.
* If no input is provided, returns the current exponentially weighted variance.
*
* @private
* @param {number} [x] - new value
* @returns {(number|null)} updated exponentially weighted variance or null
*/
function accumulator(x) {
if ( arguments.length === 0 || isnan( x ) ) {
return acc();
}
return acc( x );
}
}
// EXPORTS //
module.exports = nanewvariance;
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