rounded_percents's Introduction

Overview

Round percentages, ensuring that the results add up to 100%.

Installation

    gem "rounded_percents", git: 'https://github.com/ktopping/rounded_percents'

Usage

RoundedPercents extends Array so it responds to all the Array-like methods (e.g. [], .length, .sum, etc.)

    require 'rounded_percents'

    values = [1, 2, 3]
    RoundedPercents.new(values)
    # => [17, 33, 50]

    RoundedPercents.new(values, precision: 1)
    # => [16.7, 33.3, 50.0]

Algorithms

Specify algorithm as follows:

    RoundedPercents.new(values, algorithm: RoundedPercents::LAD)

LAD (Least Absolute Difference)

This is the default, described best here: https://stackoverflow.com/a/13483710 In short, round everything down, work out how far short of 100% the sum is, and assign this shortfall to prioritising those where it makes the "Least Absolute Difference". In practise, where precision=0, this means "in reverse order of decimal component".

LRD (Least Relative Difference)

Like the above, but tries to reassign the shortfall according to where it would make the least relative difference. Discussed here: https://stackoverflow.com/a/34959983

LRD_AVOID_ZERO (Least Relative Difference, Avoid Zero)

More of an experiment, but - like LRD BUT attempts to avoid rounding down to 0.

  RoundedPercents.new([99.5, 0.5], algorithm: RoundedPercents::LRD)
  # => [100, 0]
  RoundedPercents.new([99.5, 0.5], algorithm: RoundedPercents::LRD_AVOID_ZERO)
  # => [99, 1]

Other Algorithms (Not Implemented)

"Carry the error"

https://stackoverflow.com/a/13483486

"Thresholds"

Proposal, thresholds: [1, 5] to mean that:

All percentages that are greater that zero, but less than 1 should be displayed as "<1".
All percentages that are greater than 1, but less than 5 should display as "<5".

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