// wink-statistics
// Fast and Numerically Stable Statistical Analysis Utilities.
//
// Copyright (C) GRAYPE Systems Private Limited
//
// This file is part of “wink-statistics”.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
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// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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// DEALINGS IN THE SOFTWARE.
// ## data
// Load accessor.
var varianceXn = require( './data-varianceXn.js' );
// ### stdev
/**
*
* Comuptes the sample standard deviation of numbers contained in the `x` array.
* The computations are inspired by the method proposed by [B. P. Welford](http://dx.doi.org/10.1080/00401706.1962.10490022).
*
* @memberof data
* @param {array} x array containing 1 or more elements.
* @param {(string|number|function)} [accessor=undefined] required when elements of
* `x` are objects or arrays instead of numbers.
* For objects, use key (string) to access the value; in case of arrays, use
* index (number) to access the value; or it could be a function
* that extracts the value from the element passed to it.
* @return {number} standard deviation of sample.
* @example
* stdev( [ 2, 3, 5, 7 ] )
* // returns 2.217355782608345
* stdev( [ { x: 2 }, { x: 3 }, { x: 5 }, { x: 7 } ], 'x' )
* // returns 2.217355782608345
*/
var stdev = function ( x, accessor ) {
var vXn = varianceXn( x, accessor );
return ( vXn.size > 1 ) ? Math.sqrt( vXn.varianceXn / ( vXn.size - 1 ) ) : 0;
}; // stdev()
module.exports = stdev;