vishalbelsare / abayes

Autoregressive Bayesian linear model

Online autoregressive bayesian linear regression

This minimalist tool is dedicated to the bayesian linear regression implemented by Max Halford in his blog post Bayesian linear regression for practitioners. I slightly modified the code to obtain an autoregressive version of the original model.

For the time being, the model will systematically assume that the residues follow a normal distribution. It will be necessary to wait for the next updates of the library to include new distributions.

Bayesian linear regression has many advantages. It allows to measure the uncertainty of the model and to build confidence intervals. The simplicity of this model and its ability to answer "I don't know" makes it practical and adapted to many concrete problems.

Its online autoregressive counterpart is a nice tool for the toolbox of programmers, hackers and practitioners.

Installation:

pip install git+https://github.com/raphaelsty/abayes

Example:

Let's try to predict my ice cream consumption. I have created a dummy dataset where I record my ice cream consumption for each month of the year and for 3 years.

from abayes import dataset
df = dataset.LoadIceCream()
df.head()

We initialise the auto-regressive model with a periodicity of 24. We will use the years n-1 and n-2 to predict my ice consumption in year n.

from abayes import linear

model = linear.AbayesLr(
    p     = 24,
    alpha = 0.3,
    beta  = 1.,
)

model.learn(df['y'].values)

forecast = model.forecast(12)

lower_bound, upper_bound = model.forecast_interval(12, alpha = 0.90)

plot

import matplotlib.pyplot as plt

%config InlineBackend.figure_format = 'retina'

range_train    = range(len(df['y']))
range_forecast = range(len(df['y']), len(df['y']) + len(forecast))

fig, ax = plt.subplots(figsize=(15, 6))

ax.plot(range_train, df['y'], color='deepskyblue', label ='train')

ax.plot(range_forecast, forecast, color='red', linestyle='--', label ='forecast')

ax.fill_between(
    x     = range_forecast,
    y1    = lower_bound,
    y2    = upper_bound,
    alpha = 0.1,
    color = 'red',
    label = 'confidence'
)

plt.xticks(
    range(len(df['y']) + len(forecast)), 
    df['time'].tolist() + [f"2020/{'%02d' % i}" for i in range(1, 13)], 
    rotation='vertical'
)

ax.set_title('Quantity of ice cream')

ax.set_xlabel('Period')

ax.set_ylabel('Quantity')

ax.legend()

plt.show()

The model can also learn by mini-batch.

import numpy as np

from abayes import linear

model = linear.AbayesLr(
    p     = 24,
    alpha = 0.3,
    beta  = 1,
)

for time, y in enumerate(df['y'].values):
    
    # Online autoregressive model needs to store enough data to make a prediction (> period).
    if time > 24:
        
        lower_bound, upper_bound = model.forecast_interval(1, alpha = 0.9)
        y_pred = model.forecast(1)
        
        print('\n')
        print(f'time: {time}')
        print(f'\t y: {y}')
        print(f'\t Most likely value: {y_pred[0]:6f}')
        print(f'\t Confidence interval: [{lower_bound[0]:6f} ; {upper_bound[0]:6f}]')
    
    model.learn(np.array([y]))

time: 25
	 y: 46
	 Most likely value: 16.066921
	 Confidence interval: [-231.651593 ; 263.785435]


time: 26
	 y: 27
	 Most likely value: 50.016886
	 Confidence interval: [-179.828306 ; 279.862078]


time: 27
	 y: 30
	 Most likely value: 16.442225
	 Confidence interval: [-214.224545 ; 247.108994]


time: 28
	 y: 101
	 Most likely value: 21.766659
	 Confidence interval: [-205.891318 ; 249.424635]


time: 29
	 y: 135
	 Most likely value: 106.731389
	 Confidence interval: [-124.906692 ; 338.369470]


time: 30
	 y: 250
	 Most likely value: 143.074596
	 Confidence interval: [-75.066693 ; 361.215885]


time: 31
	 y: 210
	 Most likely value: 231.908803
	 Confidence interval: [38.905614 ; 424.911993]


time: 32
	 y: 127
	 Most likely value: 165.226916
	 Confidence interval: [-17.324602 ; 347.778435]


time: 33
	 y: 50
	 Most likely value: 78.684325
	 Confidence interval: [-75.679416 ; 233.048066]


time: 34
	 y: 14
	 Most likely value: -14.522046
	 Confidence interval: [-157.498855 ; 128.454763]


time: 35
	 y: 56
	 Most likely value: 52.063575
	 Confidence interval: [-50.776582 ; 154.903732]

License

This project is free and open-source software licensed under the MIT license.