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class SimpleLinearRegression
def initialize(xs, ys)
@xs, @ys = xs, ys
if @xs.length != @ys.length
raise "Unbalanced data. xs need to be same length as ys"
end
end
def y_intercept
mean(@ys) - (slope * mean(@xs))
end
def slope
x_mean = mean(@xs)
y_mean = mean(@ys)
numerator = (0...@xs.length).reduce(0) do |sum, i|
sum + ((@xs[i] - x_mean) * (@ys[i] - y_mean))
end
denominator = @xs.reduce(0) do |sum, x|
sum + ((x - x_mean) ** 2)
end
(numerator / denominator)
end
def mean(values)
total = values.reduce(0) { |sum, x| x + sum }
Float(total) / Float(values.length)
end
end
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