// 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.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
// ## data
// Load accessor.
var value = require( './accessor.js' );
// Load wink helpers for validation.
var helpers = require( 'wink-helpers' );
// ### Percentile
/**
*
* Returns the `q`<sup>th</sup> percentile from the `sortedData`. The computation is
* based on Method 11 described in [Quartiles in Elementary Statistics](https://ww2.amstat.org/publications/jse/v14n3/langford.html)
* by Eric Langford published in Journal of Statistics Education Volume 14, Number 3 (2006).
*
* @memberof data
* @param {array} sortedData sorted in ascending order of value.
* @param {number} q should be between 0 and 1 indicating percentile;
* for example, to get 25<sup>th</sup> percentile, it should be 0.25.
* @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.
* @returns {number} `q`<sup>th</sup> percentile of `sortedData`.
* @example
* percentile( [ 1, 1, 2, 2, 3, 3, 4, 4 ], 0.25 );
* // returns 1.25
* percentile( [ 1, 1, 2, 2, 3, 3, 4, 4 ], 0.75 );
* // returns 3.75
*/
var percentile = function ( sortedData, q, accessor ) {
if ( !helpers.array.isArray( sortedData ) || !sortedData.length ) {
throw Error( 'data-percentile: sortedData should be an array of length > 0, instead found: ' + ( typeof sortedData ) );
}
if ( ( typeof q !== 'number' ) || ( q <= 0 ) || ( q >= 1 ) ) {
throw Error( 'data-percentile: q should be a number between 0 & 1, instead found: ' + JSON.stringify( q ) );
}
// Temp variables to hold dec and int part of count*quartile respectively;
// j_1 is `j - 1`.
var g, j, j_1; // eslint-disable-line
// Data length - n plus 1.
var nP1 = sortedData.length + 1;
// The np1 x quartile - for above computation.
var nq = nP1 * q;
// Compute percentile.
j = Math.floor( nq );
g = ( nq - j ).toFixed( 2 );
j_1 = Math.max( 0, ( j - 1 ) ); // eslint-disable-line
j = Math.min( j, ( sortedData.length - 1 ) );
return ( ( ( 1 - g ) * value( sortedData[ j_1 ], accessor ) ) + ( g * value( sortedData[ j ], accessor ) ) );
}; // percentile()
module.exports = percentile;