import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import seaborn as sns

plt.rcParams['figure.figsize'] = (10, 5)
plt.style.use('fivethirtyeight')


## Fitting time series models

• Introduction to ARMAX models
• Exogenous ARMA
• Use external variables as well as time series
• ARMAX = ARMA + linear regression
• ARMAX equation
• ARMA(1, 1) model: $$y_t = a_1 y_{t-1} + m_1 \epsilon_{t-1} + \epsilon_t$$
• ARMAX(1, 1) model: $$y_t = x_1 z_t + a_1 + y_{t-1} + m_1 \epsilon_{t-1} + \epsilon_t$$

### Fitting AR and MA models

In this exercise you will fit an AR and an MA model to some data. The data here has been generated using the arma_generate_sample() function we used before.

You know the real AR and MA parameters used to create this data so it is a really good way to gain some confidence with ARMA models and know you are doing it right. In the next exercise you'll move onto some real world data with confidence.

sample = pd.read_csv('./dataset/sample.csv', index_col=0)

timeseries_1 timeseries_2
0 -0.183108 -0.183108
1 -0.245540 -0.117365
2 -0.258830 -0.218789
3 -0.279635 -0.169041
4 -0.384736 -0.282374

#### AR(2) model

from statsmodels.tsa.arima_model import ARMA

# Instantiate the model
model = ARMA(sample['timeseries_1'], order=(2, 0))

# Fit the model
results = model.fit()

# Print summary
print(results.summary())

                              ARMA Model Results
==============================================================================
Dep. Variable:           timeseries_1   No. Observations:                 1000
Model:                     ARMA(2, 0)   Log Likelihood                 148.855
Method:                       css-mle   S.D. of innovations              0.208
Date:                Mon, 15 Jun 2020   AIC                           -289.709
Time:                        18:46:18   BIC                           -270.078
Sample:                             0   HQIC                          -282.248

======================================================================================
coef    std err          z      P>|z|      [0.025      0.975]
--------------------------------------------------------------------------------------
const                 -0.0027      0.018     -0.151      0.880      -0.037       0.032
ar.L1.timeseries_1     0.8980      0.030     29.510      0.000       0.838       0.958
ar.L2.timeseries_1    -0.2704      0.030     -8.884      0.000      -0.330      -0.211
Roots
=============================================================================
Real          Imaginary           Modulus         Frequency
-----------------------------------------------------------------------------
AR.1            1.6603           -0.9702j            1.9230           -0.0842
AR.2            1.6603           +0.9702j            1.9230            0.0842
-----------------------------------------------------------------------------


#### MA(3) model

model = ARMA(sample['timeseries_2'], order=(0, 3))

# Fit the model
results = model.fit()

# Print summary
print(results.summary())

                              ARMA Model Results
==============================================================================
Dep. Variable:           timeseries_2   No. Observations:                 1000
Model:                     ARMA(0, 3)   Log Likelihood                 149.007
Method:                       css-mle   S.D. of innovations              0.208
Date:                Mon, 15 Jun 2020   AIC                           -288.014
Time:                        18:46:19   BIC                           -263.475
Sample:                             0   HQIC                          -278.687

======================================================================================
coef    std err          z      P>|z|      [0.025      0.975]
--------------------------------------------------------------------------------------
const                 -0.0018      0.012     -0.159      0.874      -0.024       0.021
ma.L1.timeseries_2     0.1995      0.031      6.352      0.000       0.138       0.261
ma.L2.timeseries_2     0.6359      0.028     22.718      0.000       0.581       0.691
ma.L3.timeseries_2    -0.0833      0.029     -2.872      0.004      -0.140      -0.026
Roots
=============================================================================
Real          Imaginary           Modulus         Frequency
-----------------------------------------------------------------------------
MA.1           -0.2389           -1.1928j            1.2165           -0.2815
MA.2           -0.2389           +1.1928j            1.2165            0.2815
MA.3            8.1089           -0.0000j            8.1089           -0.0000
-----------------------------------------------------------------------------


### Fitting an ARMA model

n this exercise you will fit an ARMA model to the earthquakes dataset. You saw before that the earthquakes dataset is stationary so you don't need to transform it at all. It comes ready for modeling straight out the ground.

earthquake = pd.read_csv('./dataset/earthquakes.csv', index_col='date', parse_dates=True)
earthquake.drop(['Year'], axis=1, inplace=True)

earthquakes_per_year
date
1900-01-01 13.0
1901-01-01 14.0
1902-01-01 8.0
1903-01-01 10.0
1904-01-01 16.0

#### ARMA(3, 1) model

model = ARMA(earthquake['earthquakes_per_year'], order=(3, 1))

# Fit the model
results = model.fit()

# Print model fit summary
print(results.summary())

                               ARMA Model Results
================================================================================
Dep. Variable:     earthquakes_per_year   No. Observations:                   99
Model:                       ARMA(3, 1)   Log Likelihood                -315.673
Method:                         css-mle   S.D. of innovations              5.853
Date:                  Mon, 15 Jun 2020   AIC                            643.345
Time:                          18:46:20   BIC                            658.916
Sample:                      01-01-1900   HQIC                           649.645
- 01-01-1998
==============================================================================================
coef    std err          z      P>|z|      [0.025      0.975]
----------------------------------------------------------------------------------------------
const                         19.6452      1.929     10.183      0.000      15.864      23.426
ar.L1.earthquakes_per_year     0.5794      0.416      1.393      0.164      -0.236       1.394
ar.L2.earthquakes_per_year     0.0251      0.208      0.121      0.904      -0.382       0.433
ar.L3.earthquakes_per_year     0.1519      0.131      1.162      0.245      -0.104       0.408
ma.L1.earthquakes_per_year    -0.1720      0.416     -0.413      0.679      -0.988       0.644
Roots
=============================================================================
Real          Imaginary           Modulus         Frequency
-----------------------------------------------------------------------------
AR.1            1.2047           -0.0000j            1.2047           -0.0000
AR.2           -0.6850           -2.2352j            2.3378           -0.2973
AR.3           -0.6850           +2.2352j            2.3378            0.2973
MA.1            5.8139           +0.0000j            5.8139            0.0000
-----------------------------------------------------------------------------

/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:162: ValueWarning: No frequency information was provided, so inferred frequency AS-JAN will be used.
% freq, ValueWarning)


### Fitting an ARMAX model

In this exercise you will fit an ARMAX model to a time series which represents the wait times at an accident and emergency room for urgent medical care.

The variable you would like to model is the wait times to be seen by a medical professional wait_times_hrs. This may be related to an exogenous variable that you measured nurse_count which is the number of nurses on shift at any given time. These can be seen below.

hospital = pd.read_csv('./dataset/hospital.csv', index_col=0, parse_dates=True)

wait_times_hrs nurse_count
2019-03-04 00:00:00 1.747261 1.0
2019-03-04 01:00:00 1.664634 1.0
2019-03-04 02:00:00 1.647047 1.0
2019-03-04 03:00:00 1.619512 1.0
2019-03-04 04:00:00 1.480415 1.0
hospital.plot(subplots=True);


This is a particularly interesting case of time series modeling as, if the number of nurses has an effect, you could change this to affect the wait times.

#### ARMAX(2, 1) model to train on the wait_times_hrs using nurse_count

model = ARMA(hospital['wait_times_hrs'], order=(2, 1), exog=hospital['nurse_count'])

# Fit the model
results = model.fit()

# Print model fit summary
print(results.summary())

                              ARMA Model Results
==============================================================================
Dep. Variable:         wait_times_hrs   No. Observations:                  168
Model:                     ARMA(2, 1)   Log Likelihood                 -11.834
Method:                       css-mle   S.D. of innovations              0.259
Date:                Mon, 15 Jun 2020   AIC                             35.668
Time:                        18:46:22   BIC                             54.411
Sample:                    03-04-2019   HQIC                            43.275
- 03-10-2019
========================================================================================
coef    std err          z      P>|z|      [0.025      0.975]
----------------------------------------------------------------------------------------
const                    2.1000      0.086     24.293      0.000       1.931       2.269
nurse_count             -0.1171      0.013     -9.054      0.000      -0.142      -0.092
ar.L1.wait_times_hrs     0.5693      0.164      3.468      0.001       0.248       0.891
ar.L2.wait_times_hrs    -0.1612      0.131     -1.226      0.220      -0.419       0.096
ma.L1.wait_times_hrs     0.3728      0.157      2.375      0.018       0.065       0.680
Roots
=============================================================================
Real          Imaginary           Modulus         Frequency
-----------------------------------------------------------------------------
AR.1            1.7656           -1.7566j            2.4906           -0.1246
AR.2            1.7656           +1.7566j            2.4906            0.1246
MA.1           -2.6827           +0.0000j            2.6827            0.5000
-----------------------------------------------------------------------------

/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:162: ValueWarning: No frequency information was provided, so inferred frequency H will be used.
% freq, ValueWarning)


## Forecasting

### Generating one-step-ahead predictions

It is very hard to forecast stock prices. Classic economics actually tells us that this should be impossible because of market clearing.

Your task in this exercise is to attempt the impossible and predict the Amazon stock price anyway.

In this exercise you will generate one-step-ahead predictions for the stock price as well as the uncertainty of these predictions.

amazon = pd.read_csv('./dataset/amazon_close.csv', parse_dates=True, index_col='date')
amazon = amazon.iloc[::-1]

from statsmodels.tsa.statespace.sarimax import SARIMAX

model = SARIMAX(amazon.loc['2018-01-01':'2019-02-08'], order=(3, 1, 3), seasonal_order=(1, 0, 1, 7),
enforce_invertibility=False,
enforce_stationarity=False,
simple_differencing=False,
measurement_error=False,
k_trend=0)
results = model.fit()

/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:218: ValueWarning: A date index has been provided, but it has no associated frequency information and so will be ignored when e.g. forecasting.
' ignored when e.g. forecasting.', ValueWarning)
/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:218: ValueWarning: A date index has been provided, but it has no associated frequency information and so will be ignored when e.g. forecasting.
' ignored when e.g. forecasting.', ValueWarning)
/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/base/model.py:568: ConvergenceWarning: Maximum Likelihood optimization failed to converge. Check mle_retvals
"Check mle_retvals", ConvergenceWarning)

results.summary()

Dep. Variable: No. Observations: close 278 SARIMAX(3, 1, 3)x(1, 0, [1], 7) -1338.384 Mon, 15 Jun 2020 2694.769 18:46:24 2727.020 0 2707.726 - 278 opg
coef std err z P>|z| [0.025 0.975] 0.1074 0.048 2.258 0.024 0.014 0.201 0.0521 0.038 1.359 0.174 -0.023 0.127 -0.8974 0.042 -21.606 0.000 -0.979 -0.816 -0.1125 0.036 -3.113 0.002 -0.183 -0.042 -0.1496 0.041 -3.671 0.000 -0.229 -0.070 0.9763 0.032 30.611 0.000 0.914 1.039 0.1821 0.675 0.270 0.787 -1.141 1.506 -0.2247 0.666 -0.337 0.736 -1.531 1.081 1319.0972 99.104 13.310 0.000 1124.858 1513.337
 Ljung-Box (Q): Jarque-Bera (JB): 28.84 22.02 0.91 0 3.1 -0.35 0 4.23

Warnings:
[1] Covariance matrix calculated using the outer product of gradients (complex-step).
one_step_forecast = results.get_prediction(start=-30)

# Extract prediction mean
mean_forecast = one_step_forecast.predicted_mean

# Get confidence intervals of predictions
confidence_intervals = one_step_forecast.conf_int()

# Select lower and upper confidence limits
lower_limits = confidence_intervals.loc[:,'lower close']
upper_limits = confidence_intervals.loc[:,'upper close']

# Print best estimate  predictions
print(mean_forecast.values)

[1475.3973982  1462.84752096 1470.99540557 1498.12115484 1537.51838107
1508.09054892 1581.14926322 1627.24259216 1650.12797834 1649.53776158
1657.7163931  1648.12485235 1625.78085085 1671.04311494 1672.23342965
1683.43565237 1693.6949342  1642.5733451  1657.25345019 1652.28661236
1661.06421713 1620.90897063 1594.76080937 1679.5496602  1724.90278402
1629.30624018 1638.13065893 1647.51124676 1636.55265666 1606.68029738]


### Plotting one-step-ahead predictions

Now that you have your predictions on the Amazon stock, you should plot these predictions to see how you've done.

You made predictions over the latest 30 days of data available, always forecasting just one day ahead. By evaluating these predictions you can judge how the model performs in making predictions for just the next day, where you don't know the answer.

plt.plot(amazon.index, amazon['close'], label='observed');

# Plot your mean predictions
plt.plot(mean_forecast.index, mean_forecast, color='r', label='forecast');

# shade the area between your confidence limits
plt.fill_between(lower_limits.index, lower_limits, upper_limits, color='pink');

# Set labels, legends
plt.xlabel('Date');
plt.ylabel('Amazon Stock Price - Close USD');
plt.legend();


### Generating dynamic forecasts

Now lets move a little further into the future, to dynamic predictions. What if you wanted to predict the Amazon stock price, not just for tomorrow, but for next week or next month? This is where dynamical predictions come in.

Remember that in the video you learned how it is more difficult to make precise long-term forecasts because the shock terms add up. The further into the future the predictions go, the more uncertain. This is especially true with stock data and so you will likely find that your predictions in this exercise are not as precise as those in the last exercise.

dynamic_forecast = results.get_prediction(start=-30, dynamic=True)

# Extract prediction mean
mean_forecast = dynamic_forecast.predicted_mean

# Get confidence intervals of predictions
confidence_intervals = dynamic_forecast.conf_int()

# Select lower and upper confidence limits
lower_limits = confidence_intervals.loc[:, 'lower close']
upper_limits = confidence_intervals.loc[:, 'upper close']

# Print bet estimate predictions
print(mean_forecast.values)

[1475.3973982  1476.40017466 1468.3901068  1467.14976272 1468.18656451
1478.14922455 1476.87176087 1480.11773026 1472.62955383 1469.88023553
1466.93794607 1473.65129549 1477.18299701 1479.91259781 1475.05662359
1471.72120655 1468.06637732 1471.97702823 1475.28213547 1479.2113115
1476.17980423 1473.21901888 1469.25578864 1471.28791358 1473.97822619
1477.94469229 1476.70394567 1474.34205877 1470.48718766 1471.07043809]


### Plotting dynamic forecasts

Time to plot your predictions. Remember that making dynamic predictions, means that your model makes predictions with no corrections, unlike the one-step-ahead predictions. This is kind of like making a forecast now for the next 30 days, and then waiting to see what happens before comparing how good your predictions were.

plt.plot(amazon.index, amazon['close'], label='observed');

# Plot your mean forecast
plt.plot(mean_forecast.index, mean_forecast, label='forecast');

# Shade the area between your confidence limits
plt.fill_between(lower_limits.index, lower_limits, upper_limits, color='pink');

# set labels, legends
plt.xlabel('Date');
plt.ylabel('Amazon Stock Price - Close USD');
plt.legend();


## Intro to ARIMA models

• The ARIMA model
• Take the difference
• Fit ARMA model
• Integrate forecast
• ARIMA - Autoregressive Integrated Moving Average

### Differencing and fitting ARMA

In this exercise you will fit an ARMA model to the Amazon stocks dataset. As you saw before, this is a non-stationary dataset. You will use differencing to make it stationary so that you can fit an ARMA model.

In the next section you'll make a forecast of the differences and use this to forecast the actual values.

amazon_diff = amazon.diff().dropna()

# Create ARMA(2, 2) model
arma = SARIMAX(amazon_diff, order=(2, 0, 2))

# Fit model
arma_results = arma.fit()

# Print fit summary
print(arma_results.summary())

/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:218: ValueWarning: A date index has been provided, but it has no associated frequency information and so will be ignored when e.g. forecasting.
' ignored when e.g. forecasting.', ValueWarning)
/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:218: ValueWarning: A date index has been provided, but it has no associated frequency information and so will be ignored when e.g. forecasting.
' ignored when e.g. forecasting.', ValueWarning)

                               SARIMAX Results
==============================================================================
Dep. Variable:                  close   No. Observations:                 1258
Model:               SARIMAX(2, 0, 2)   Log Likelihood               -5531.159
Date:                Mon, 15 Jun 2020   AIC                          11072.319
Time:                        18:46:30   BIC                          11098.005
Sample:                             0   HQIC                         11081.972
- 1258
Covariance Type:                  opg
==============================================================================
coef    std err          z      P>|z|      [0.025      0.975]
------------------------------------------------------------------------------
ar.L1          1.0770      0.004    259.224      0.000       1.069       1.085
ar.L2         -0.9950      0.004   -273.566      0.000      -1.002      -0.988
ma.L1         -1.0915      0.006   -177.349      0.000      -1.104      -1.079
ma.L2          0.9946      0.007    145.386      0.000       0.981       1.008
sigma2       391.6344      6.804     57.556      0.000     378.298     404.971
===================================================================================
Ljung-Box (Q):                      104.43   Jarque-Bera (JB):              6865.60
Prob(Q):                              0.00   Prob(JB):                         0.00
Heteroskedasticity (H):              15.47   Skew:                            -0.20
Prob(H) (two-sided):                  0.00   Kurtosis:                        14.44
===================================================================================

Warnings:
[1] Covariance matrix calculated using the outer product of gradients (complex-step).


### Unrolling ARMA forecast

Now you will use the model that you trained in the previous exercise arma in order to forecast the absolute value of the Amazon stocks dataset. Remember that sometimes predicting the difference could be enough; will the stocks go up, or down; but sometimes the absolute value is key.

arma_diff_forecast = arma_results.get_forecast(steps=10).predicted_mean

# Integrate the difference forecast
arma_int_forecast = np.cumsum(arma_diff_forecast)

# Make absolute value forecast
arma_value_forecast = arma_int_forecast + amazon.iloc[-1, 0]

# Print forecast
print(arma_value_forecast)

1258    1593.660837
1259    1601.964525
1260    1605.494152
1261    1601.033697
1262    1592.717948
1263    1588.199887
1264    1591.607802
1265    1599.773421
1266    1605.177031
1267    1602.872224
dtype: float64

/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:583: ValueWarning: No supported index is available. Prediction results will be given with an integer index beginning at start.
ValueWarning)


### Fitting an ARIMA model

In this exercise you'll learn how to be lazy in time series modeling. Instead of taking the difference, modeling the difference and then integrating, you're just going to lets statsmodels do the hard work for you.

You'll repeat the same exercise that you did before, of forecasting the absolute values of the Amazon stocks dataset, but this time with an ARIMA model.

arima = SARIMAX(amazon, order=(2, 1, 2))

# Fit ARIMA model
arima_results = arima.fit()

# Make ARIMA forecast of next 10 values
arima_value_forecast = arima_results.get_forecast(steps=10).predicted_mean

# Print forecast
print(arima_value_forecast)

/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:218: ValueWarning: A date index has been provided, but it has no associated frequency information and so will be ignored when e.g. forecasting.
' ignored when e.g. forecasting.', ValueWarning)
/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:218: ValueWarning: A date index has been provided, but it has no associated frequency information and so will be ignored when e.g. forecasting.
' ignored when e.g. forecasting.', ValueWarning)

1259    1593.662417
1260    1601.932909
1261    1605.426182
1262    1600.960117
1263    1592.674090
1264    1588.192669
1265    1591.609853
1266    1599.749278
1267    1605.116372
1268    1602.799012
dtype: float64

/home/chanseok/anaconda3/lib/python3.7/site-packages/statsmodels/tsa/base/tsa_model.py:583: ValueWarning: No supported index is available. Prediction results will be given with an integer index beginning at start.
ValueWarning)

plt.plot(amazon.index[-100:], amazon.iloc[-100:]['close'], label='observed');

# Plot your mean forecast
rng = pd.date_range(start='2019-02-08', end='2019-02-21', freq='b')
plt.plot(rng, arima_value_forecast.values, label='forecast');

# Shade the area between your confidence limits
# plt.fill_between(lower_limits.index, lower_limits, upper_limits, color='pink');

# set labels, legends
plt.xlabel('Date');
plt.ylabel('Amazon Stock Price - Close USD');
plt.legend();
plt.savefig('../images/arima_forecast.png')