chromium / chromium / src / 39709d9f02fcb5c6b746e773b6c48b8e6855819e / . / tools / auto_bisect / math_utils.py

# Copyright 2014 The Chromium Authors. All rights reserved. | |

# Use of this source code is governed by a BSD-style license that can be | |

# found in the LICENSE file. | |

"""General statistical or mathematical functions.""" | |

import math | |

def TruncatedMean(data_set, truncate_proportion): | |

"""Calculates the truncated mean of a set of values. | |

Note that this isn't just the mean of the set of values with the highest | |

and lowest values discarded; the non-discarded values are also weighted | |

differently depending how many values are discarded. | |

NOTE: If there's not much benefit from this keeping and weighting | |

partial values, it might be better to use a simplified truncated mean | |

function without weighting. | |

Args: | |

data_set: Non-empty list of values. | |

truncate_proportion: How much of the upper and lower portions of the data | |

set to discard, expressed as a value in the range [0, 1]. | |

Note: a value of 0.5 or greater would be meaningless | |

Returns: | |

The truncated mean as a float. | |

Raises: | |

TypeError: The data set was empty after discarding values. | |

""" | |

if len(data_set) > 2: | |

data_set = sorted(data_set) | |

discard_num_float = len(data_set) * truncate_proportion | |

discard_num_int = int(math.floor(discard_num_float)) | |

kept_weight = len(data_set) - (discard_num_float * 2) | |

data_set = data_set[discard_num_int:len(data_set)-discard_num_int] | |

weight_left = 1.0 - (discard_num_float - discard_num_int) | |

if weight_left < 1: | |

# If the % to discard leaves a fractional portion, need to weight those | |

# values. | |

unweighted_vals = data_set[1:len(data_set)-1] | |

weighted_vals = [data_set[0], data_set[len(data_set)-1]] | |

weighted_vals = [w * weight_left for w in weighted_vals] | |

data_set = weighted_vals + unweighted_vals | |

else: | |

kept_weight = len(data_set) | |

data_sum = reduce(lambda x, y: float(x) + float(y), data_set) | |

truncated_mean = data_sum / kept_weight | |

return truncated_mean | |

def Mean(values): | |

"""Calculates the arithmetic mean of a list of values.""" | |

return TruncatedMean(values, 0.0) | |

def Variance(values): | |

"""Calculates the sample variance.""" | |

if len(values) == 1: | |

return 0.0 | |

mean = Mean(values) | |

differences_from_mean = [float(x) - mean for x in values] | |

squared_differences = [float(x * x) for x in differences_from_mean] | |

variance = sum(squared_differences) / (len(values) - 1) | |

return variance | |

def StandardDeviation(values): | |

"""Calculates the sample standard deviation of the given list of values.""" | |

return math.sqrt(Variance(values)) | |

def RelativeChange(before, after): | |

"""Returns the relative change of before and after, relative to before. | |

There are several different ways to define relative difference between | |

two numbers; sometimes it is defined as relative to the smaller number, | |

or to the mean of the two numbers. This version returns the difference | |

relative to the first of the two numbers. | |

Args: | |

before: A number representing an earlier value. | |

after: Another number, representing a later value. | |

Returns: | |

A non-negative floating point number; 0.1 represents a 10% change. | |

""" | |

if before == after: | |

return 0.0 | |

if before == 0: | |

return float('nan') | |

difference = after - before | |

return math.fabs(difference / before) | |

def PooledStandardError(work_sets): | |

"""Calculates the pooled sample standard error for a set of samples. | |

Args: | |

work_sets: A collection of collections of numbers. | |

Returns: | |

Pooled sample standard error. | |

""" | |

numerator = 0.0 | |

denominator1 = 0.0 | |

denominator2 = 0.0 | |

for current_set in work_sets: | |

std_dev = StandardDeviation(current_set) | |

numerator += (len(current_set) - 1) * std_dev ** 2 | |

denominator1 += len(current_set) - 1 | |

if len(current_set) > 0: | |

denominator2 += 1.0 / len(current_set) | |

if denominator1 == 0: | |

return 0.0 | |

return math.sqrt(numerator / denominator1) * math.sqrt(denominator2) | |

# Redefining built-in 'StandardError' | |

# pylint: disable=W0622 | |

def StandardError(values): | |

"""Calculates the standard error of a list of values.""" | |

# NOTE: This behavior of returning 0.0 in the case of an empty list is | |

# inconsistent with Variance and StandardDeviation above. | |

if len(values) <= 1: | |

return 0.0 | |

std_dev = StandardDeviation(values) | |

return std_dev / math.sqrt(len(values)) |