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require 'more_core_extensions/core_ext/numeric/math'
module MoreCoreExtensions
module MathSlope
module ClassMethods
# Finds the y coordinate given x, slope of the line and the y intercept
#
# `y = mx + b`
# Where `m` is the slope of the line and `b` is the y intercept
#
# Math.slope_y_intercept(1, 0.5, 1) # => 1.5
def slope_y_intercept(x, slope, y_intercept)
slope * x + y_intercept
end
# Finds the x coordinate given y, slope of the line and the y intercept
#
# `x = (y - b) / m`
# Where `m` is the slope of the line and `b` is the y intercept
#
# Math.slope_x_intercept(1.5, 0.5, 1) # => 1.0
def slope_x_intercept(y, slope, y_intercept)
(y - y_intercept) / slope.to_f
end
# Finds the linear regression of the given coordinates. Coordinates should be given as x, y pairs.
#
# Returns the slope of the line, the y intercept, and the R-squared value.
#
# Math.linear_regression([1.0, 1.0], [2.0, 2.0]) # => [1.0, 0.0, 1.0]
def linear_regression(*coordinates)
return if coordinates.empty?
x_array, y_array = coordinates.transpose
sum_x = x_array.sum
sum_x2 = x_array.map(&:square).sum
sum_y = y_array.sum
sum_y2 = y_array.map(&:square).sum
sum_xy = coordinates.map { |x, y| x * y }.sum
n = coordinates.size.to_f
slope = (n * sum_xy - sum_x * sum_y) / (n * sum_x2 - sum_x.square)
return if slope.nan?
y_intercept = (sum_y - slope * sum_x) / n
r_squared = (n * sum_xy - sum_x * sum_y) / Math.sqrt((n * sum_x2 - sum_x.square) * (n * sum_y2 - sum_y.square)) rescue nil
return slope, y_intercept, r_squared
end
end
end
end
Math.send(:extend, MoreCoreExtensions::MathSlope::ClassMethods)
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9 entries across 9 versions & 1 rubygems